HID: uclogic: Extract tablet parameter discovery into a module

Refactor and extract UC-Logic tablet initialization and parameter
discovery into a module. For these tablets, the major part of parameter
discovery cannot be separated from initialization so they have to be in
the same module. Define explicitly and clearly what possible quirks the
tablets may have to make the driver implementation easier and simpler.

Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

4 files changed, 1090 insertions, 327 deletions

diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
index fb75366ea776..9b3a747af60d 100644
--- a/drivers/hid/Makefile
+++ b/drivers/hid/Makefile
@@ -109,7 +109,8 @@ obj-$(CONFIG_HID_TIVO)		+= hid-tivo.o
 obj-$(CONFIG_HID_TOPSEED)	+= hid-topseed.o
 obj-$(CONFIG_HID_TWINHAN)	+= hid-twinhan.o
 hid-uclogic-objs		:= hid-uclogic-core.o \
-				   hid-uclogic-rdesc.o
+				   hid-uclogic-rdesc.o \
+				   hid-uclogic-params.o
 obj-$(CONFIG_HID_UCLOGIC)	+= hid-uclogic.o
 obj-$(CONFIG_HID_UDRAW_PS3)	+= hid-udraw-ps3.o
 obj-$(CONFIG_HID_LED)		+= hid-led.o
diff --git a/drivers/hid/hid-uclogic-core.c b/drivers/hid/hid-uclogic-core.c
index 4042183ee9a3..72a3a43766cc 100644
--- a/drivers/hid/hid-uclogic-core.c
+++ b/drivers/hid/hid-uclogic-core.c
@@ -16,126 +16,48 @@
 #include <linux/device.h>
 #include <linux/hid.h>
 #include <linux/module.h>
-#include <linux/usb.h>
 #include "usbhid/usbhid.h"
-#include "hid-uclogic-rdesc.h"
+#include "hid-uclogic-params.h"
 
 #include "hid-ids.h"
 
-/* Parameter indices */
-enum uclogic_prm {
-	UCLOGIC_PRM_X_LM	= 1,
-	UCLOGIC_PRM_Y_LM	= 2,
-	UCLOGIC_PRM_PRESSURE_LM	= 4,
-	UCLOGIC_PRM_RESOLUTION	= 5,
-	UCLOGIC_PRM_NUM
-};
-
 /* Driver data */
 struct uclogic_drvdata {
-	__u8 *rdesc;
-	unsigned int rsize;
-	bool invert_pen_inrange;
-	bool ignore_pen_usage;
-	bool has_virtual_pad_interface;
+	/* Interface parameters */
+	struct uclogic_params params;
+	/* Pointer to the replacement report descriptor. NULL if none. */
+	__u8 *desc_ptr;
+	/*
+	 * Size of the replacement report descriptor.
+	 * Only valid if desc_ptr is not NULL
+	 */
+	unsigned int desc_size;
 };
 
 static __u8 *uclogic_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 					unsigned int *rsize)
 {
-	struct usb_interface *iface = to_usb_interface(hdev->dev.parent);
-	__u8 iface_num = iface->cur_altsetting->desc.bInterfaceNumber;
 	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
 
-	if (drvdata->rdesc != NULL) {
-		rdesc = drvdata->rdesc;
-		*rsize = drvdata->rsize;
-		return rdesc;
-	}
-
-	switch (hdev->product) {
-	case USB_DEVICE_ID_UCLOGIC_TABLET_PF1209:
-		if (*rsize == UCLOGIC_RDESC_PF1209_ORIG_SIZE) {
-			rdesc = uclogic_rdesc_pf1209_fixed_arr;
-			*rsize = uclogic_rdesc_pf1209_fixed_size;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_WP4030U:
-		if (*rsize == UCLOGIC_RDESC_WPXXXXU_ORIG_SIZE) {
-			rdesc = uclogic_rdesc_wp4030u_fixed_arr;
-			*rsize = uclogic_rdesc_wp4030u_fixed_size;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_WP5540U:
-		if (*rsize == UCLOGIC_RDESC_WPXXXXU_ORIG_SIZE) {
-			rdesc = uclogic_rdesc_wp5540u_fixed_arr;
-			*rsize = uclogic_rdesc_wp5540u_fixed_size;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_WP8060U:
-		if (*rsize == UCLOGIC_RDESC_WPXXXXU_ORIG_SIZE) {
-			rdesc = uclogic_rdesc_wp8060u_fixed_arr;
-			*rsize = uclogic_rdesc_wp8060u_fixed_size;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_WP1062:
-		if (*rsize == UCLOGIC_RDESC_WP1062_ORIG_SIZE) {
-			rdesc = uclogic_rdesc_wp1062_fixed_arr;
-			*rsize = uclogic_rdesc_wp1062_fixed_size;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_WIRELESS_TABLET_TWHL850:
-		switch (iface_num) {
-		case 0:
-			if (*rsize == UCLOGIC_RDESC_TWHL850_ORIG0_SIZE) {
-				rdesc = uclogic_rdesc_twhl850_fixed0_arr;
-				*rsize = uclogic_rdesc_twhl850_fixed0_size;
-			}
-			break;
-		case 1:
-			if (*rsize == UCLOGIC_RDESC_TWHL850_ORIG1_SIZE) {
-				rdesc = uclogic_rdesc_twhl850_fixed1_arr;
-				*rsize = uclogic_rdesc_twhl850_fixed1_size;
-			}
-			break;
-		case 2:
-			if (*rsize == UCLOGIC_RDESC_TWHL850_ORIG2_SIZE) {
-				rdesc = uclogic_rdesc_twhl850_fixed2_arr;
-				*rsize = uclogic_rdesc_twhl850_fixed2_size;
-			}
-			break;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_TWHA60:
-		switch (iface_num) {
-		case 0:
-			if (*rsize == UCLOGIC_RDESC_TWHA60_ORIG0_SIZE) {
-				rdesc = uclogic_rdesc_twha60_fixed0_arr;
-				*rsize = uclogic_rdesc_twha60_fixed0_size;
-			}
-			break;
-		case 1:
-			if (*rsize == UCLOGIC_RDESC_TWHA60_ORIG1_SIZE) {
-				rdesc = uclogic_rdesc_twha60_fixed1_arr;
-				*rsize = uclogic_rdesc_twha60_fixed1_size;
-			}
-			break;
-		}
-		break;
+	if (drvdata->desc_ptr != NULL) {
+		rdesc = drvdata->desc_ptr;
+		*rsize = drvdata->desc_size;
 	}
-
 	return rdesc;
 }
 
-static int uclogic_input_mapping(struct hid_device *hdev, struct hid_input *hi,
-		struct hid_field *field, struct hid_usage *usage,
-		unsigned long **bit, int *max)
+static int uclogic_input_mapping(struct hid_device *hdev,
+				 struct hid_input *hi,
+				 struct hid_field *field,
+				 struct hid_usage *usage,
+				 unsigned long **bit,
+				 int *max)
 {
 	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
+	struct uclogic_params *params = &drvdata->params;
 
 	/* discard the unused pen interface */
-	if ((drvdata->ignore_pen_usage) &&
-	    (field->application == HID_DG_PEN))
+	if (params->pen_unused && (field->application == HID_DG_PEN))
 		return -1;
 
 	/* let hid-core decide what to do */
@@ -189,160 +111,12 @@ static int uclogic_input_configured(struct hid_device *hdev,
 	return 0;
 }
 
-/**
- * Enable fully-functional tablet mode and determine device parameters.
- *
- * @hdev:	HID device
- */
-static int uclogic_tablet_enable(struct hid_device *hdev)
-{
-	int rc;
-	struct usb_device *usb_dev = hid_to_usb_dev(hdev);
-	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
-	__le16 *buf = NULL;
-	size_t len;
-	s32 params[UCLOGIC_RDESC_PEN_PH_ID_NUM];
-	s32 resolution;
-
-	/*
-	 * Read string descriptor containing tablet parameters. The specific
-	 * string descriptor and data were discovered by sniffing the Windows
-	 * driver traffic.
-	 * NOTE: This enables fully-functional tablet mode.
-	 */
-	len = UCLOGIC_PRM_NUM * sizeof(*buf);
-	buf = kmalloc(len, GFP_KERNEL);
-	if (buf == NULL) {
-		rc = -ENOMEM;
-		goto cleanup;
-	}
-	rc = usb_control_msg(usb_dev, usb_rcvctrlpipe(usb_dev, 0),
-				USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
-				(USB_DT_STRING << 8) + 0x64,
-				0x0409, buf, len,
-				USB_CTRL_GET_TIMEOUT);
-	if (rc == -EPIPE) {
-		hid_err(hdev, "device parameters not found\n");
-		rc = -ENODEV;
-		goto cleanup;
-	} else if (rc < 0) {
-		hid_err(hdev, "failed to get device parameters: %d\n", rc);
-		rc = -ENODEV;
-		goto cleanup;
-	} else if (rc != len) {
-		hid_err(hdev, "invalid device parameters\n");
-		rc = -ENODEV;
-		goto cleanup;
-	}
-
-	/* Extract device parameters */
-	params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] =
-		le16_to_cpu(buf[UCLOGIC_PRM_X_LM]);
-	params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] =
-		le16_to_cpu(buf[UCLOGIC_PRM_Y_LM]);
-	params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] =
-		le16_to_cpu(buf[UCLOGIC_PRM_PRESSURE_LM]);
-	resolution = le16_to_cpu(buf[UCLOGIC_PRM_RESOLUTION]);
-	if (resolution == 0) {
-		params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0;
-		params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0;
-	} else {
-		params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] =
-			params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] *
-			1000 / resolution;
-		params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] =
-			params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] *
-			1000 / resolution;
-	}
-
-	/* Format fixed report descriptor */
-	drvdata->rdesc = uclogic_rdesc_template_apply(
-				uclogic_rdesc_pen_template_arr,
-				uclogic_rdesc_pen_template_size,
-				params, ARRAY_SIZE(params));
-	if (drvdata->rdesc == NULL) {
-		rc = -ENOMEM;
-		goto cleanup;
-	}
-	drvdata->rsize = uclogic_rdesc_pen_template_size;
-
-	rc = 0;
-
-cleanup:
-	kfree(buf);
-	return rc;
-}
-
-/**
- * Enable actual button mode.
- *
- * @hdev:	HID device
- */
-static int uclogic_button_enable(struct hid_device *hdev)
-{
-	int rc;
-	struct usb_device *usb_dev = hid_to_usb_dev(hdev);
-	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
-	char *str_buf;
-	size_t str_len = 16;
-	unsigned char *rdesc;
-	size_t rdesc_len;
-
-	str_buf = kzalloc(str_len, GFP_KERNEL);
-	if (str_buf == NULL) {
-		rc = -ENOMEM;
-		goto cleanup;
-	}
-
-	/* Enable abstract keyboard mode */
-	rc = usb_string(usb_dev, 0x7b, str_buf, str_len);
-	if (rc == -EPIPE) {
-		hid_info(hdev, "button mode setting not found\n");
-		rc = 0;
-		goto cleanup;
-	} else if (rc < 0) {
-		hid_err(hdev, "failed to enable abstract keyboard\n");
-		goto cleanup;
-	} else if (strncmp(str_buf, "HK On", rc)) {
-		hid_info(hdev, "invalid answer when requesting buttons: '%s'\n",
-			str_buf);
-		rc = -EINVAL;
-		goto cleanup;
-	}
-
-	/* Re-allocate fixed report descriptor */
-	rdesc_len = drvdata->rsize + uclogic_rdesc_buttonpad_size;
-	rdesc = devm_kzalloc(&hdev->dev, rdesc_len, GFP_KERNEL);
-	if (!rdesc) {
-		rc = -ENOMEM;
-		goto cleanup;
-	}
-
-	memcpy(rdesc, drvdata->rdesc, drvdata->rsize);
-
-	/* Append the buttonpad descriptor */
-	memcpy(rdesc + drvdata->rsize, uclogic_rdesc_buttonpad_arr,
-	       uclogic_rdesc_buttonpad_size);
-
-	/* clean up old rdesc and use the new one */
-	drvdata->rsize = rdesc_len;
-	devm_kfree(&hdev->dev, drvdata->rdesc);
-	drvdata->rdesc = rdesc;
-
-	rc = 0;
-
-cleanup:
-	kfree(str_buf);
-	return rc;
-}
-
 static int uclogic_probe(struct hid_device *hdev,
 		const struct hid_device_id *id)
 {
 	int rc;
-	struct usb_interface *intf = to_usb_interface(hdev->dev.parent);
-	struct usb_device *udev = hid_to_usb_dev(hdev);
-	struct uclogic_drvdata *drvdata;
+	struct uclogic_drvdata *drvdata = NULL;
+	bool params_initialized = false;
 
 	/*
 	 * libinput requires the pad interface to be on a different node
@@ -352,104 +126,97 @@ static int uclogic_probe(struct hid_device *hdev,
 
 	/* Allocate and assign driver data */
 	drvdata = devm_kzalloc(&hdev->dev, sizeof(*drvdata), GFP_KERNEL);
-	if (drvdata == NULL)
-		return -ENOMEM;
-
+	if (drvdata == NULL) {
+		rc = -ENOMEM;
+		goto failure;
+	}
 	hid_set_drvdata(hdev, drvdata);
 
-	switch (id->product) {
-	case USB_DEVICE_ID_HUION_TABLET:
-	case USB_DEVICE_ID_YIYNOVA_TABLET:
-	case USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_81:
-	case USB_DEVICE_ID_UCLOGIC_DRAWIMAGE_G3:
-	case USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_45:
-		/* If this is the pen interface */
-		if (intf->cur_altsetting->desc.bInterfaceNumber == 0) {
-			rc = uclogic_tablet_enable(hdev);
-			if (rc) {
-				hid_err(hdev, "tablet enabling failed\n");
-				return rc;
-			}
-			drvdata->invert_pen_inrange = true;
-
-			rc = uclogic_button_enable(hdev);
-			drvdata->has_virtual_pad_interface = !rc;
-		} else {
-			drvdata->ignore_pen_usage = true;
-		}
-		break;
-	case USB_DEVICE_ID_UGTIZER_TABLET_GP0610:
-	case USB_DEVICE_ID_UGEE_TABLET_EX07S:
-		/* If this is the pen interface */
-		if (intf->cur_altsetting->desc.bInterfaceNumber == 1) {
-			rc = uclogic_tablet_enable(hdev);
-			if (rc) {
-				hid_err(hdev, "tablet enabling failed\n");
-				return rc;
-			}
-			drvdata->invert_pen_inrange = true;
-		} else {
-			drvdata->ignore_pen_usage = true;
-		}
-		break;
-	case USB_DEVICE_ID_UCLOGIC_TABLET_TWHA60:
-		/*
-		 * If it is the three-interface version, which is known to
-		 * respond to initialization.
-		 */
-		if (udev->config->desc.bNumInterfaces == 3) {
-			/* If it is the pen interface */
-			if (intf->cur_altsetting->desc.bInterfaceNumber == 0) {
-				rc = uclogic_tablet_enable(hdev);
-				if (rc) {
-					hid_err(hdev, "tablet enabling failed\n");
-					return rc;
-				}
-				drvdata->invert_pen_inrange = true;
+	/* Initialize the device and retrieve interface parameters */
+	rc = uclogic_params_init(&drvdata->params, hdev);
+	if (rc != 0) {
+		hid_err(hdev, "failed probing parameters: %d\n", rc);
+		goto failure;
+	}
+	params_initialized = true;
+	hid_dbg(hdev, "parameters:\n" UCLOGIC_PARAMS_FMT_STR,
+		UCLOGIC_PARAMS_FMT_ARGS(&drvdata->params));
+	if (drvdata->params.invalid) {
+		hid_info(hdev, "interface is invalid, ignoring\n");
+		rc = -ENODEV;
+		goto failure;
+	}
 
-				rc = uclogic_button_enable(hdev);
-				drvdata->has_virtual_pad_interface = !rc;
-			} else {
-				drvdata->ignore_pen_usage = true;
-			}
-		}
-		break;
+	/* Generate replacement report descriptor */
+	rc = uclogic_params_get_desc(&drvdata->params,
+				     &drvdata->desc_ptr,
+				     &drvdata->desc_size);
+	if (rc) {
+		hid_err(hdev,
+			"failed generating replacement report descriptor: %d\n",
+			rc);
+		goto failure;
 	}
 
 	rc = hid_parse(hdev);
 	if (rc) {
 		hid_err(hdev, "parse failed\n");
-		return rc;
+		goto failure;
 	}
 
 	rc = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
 	if (rc) {
 		hid_err(hdev, "hw start failed\n");
-		return rc;
+		goto failure;
 	}
 
 	return 0;
+failure:
+	/* Assume "remove" might not be called if "probe" failed */
+	if (params_initialized)
+		uclogic_params_cleanup(&drvdata->params);
+	return rc;
 }
 
-static int uclogic_raw_event(struct hid_device *hdev, struct hid_report *report,
-			u8 *data, int size)
+static int uclogic_raw_event(struct hid_device *hdev,
+				struct hid_report *report,
+				u8 *data, int size)
 {
 	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
+	struct uclogic_params *params = &drvdata->params;
 
-	if ((report->type == HID_INPUT_REPORT) &&
-	    (report->id == UCLOGIC_RDESC_PEN_ID) &&
+	/* Tweak pen reports, if necessary */
+	if (!params->pen_unused &&
+	    (report->type == HID_INPUT_REPORT) &&
+	    (report->id == params->pen.id) &&
 	    (size >= 2)) {
-		if (drvdata->has_virtual_pad_interface && (data[1] & 0x20))
-			/* Change to virtual frame button report ID */
-			data[0] = 0xf7;
-		else if (drvdata->invert_pen_inrange)
+		/* If it's the "virtual" frame controls report */
+		if (params->frame.id != 0 &&
+		    data[1] & params->pen_frame_flag) {
+			/* Change to virtual frame controls report ID */
+			data[0] = params->frame.id;
+			return 0;
+		}
+		/* If in-range reports are inverted */
+		if (params->pen.inrange ==
+			UCLOGIC_PARAMS_PEN_INRANGE_INVERTED) {
 			/* Invert the in-range bit */
 			data[1] ^= 0x40;
+		}
 	}
 
 	return 0;
 }
 
+static void uclogic_remove(struct hid_device *hdev)
+{
+	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
+
+	hid_hw_stop(hdev);
+	kfree(drvdata->desc_ptr);
+	uclogic_params_cleanup(&drvdata->params);
+}
+
 static const struct hid_device_id uclogic_devices[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
 				USB_DEVICE_ID_UCLOGIC_TABLET_PF1209) },
@@ -465,14 +232,22 @@ static const struct hid_device_id uclogic_devices[] = {
 				USB_DEVICE_ID_UCLOGIC_WIRELESS_TABLET_TWHL850) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
 				USB_DEVICE_ID_UCLOGIC_TABLET_TWHA60) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_HUION, USB_DEVICE_ID_HUION_TABLET) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC, USB_DEVICE_ID_HUION_TABLET) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC, USB_DEVICE_ID_YIYNOVA_TABLET) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC, USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_81) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC, USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_45) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC, USB_DEVICE_ID_UCLOGIC_DRAWIMAGE_G3) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UGTIZER, USB_DEVICE_ID_UGTIZER_TABLET_GP0610) },
-	{ HID_USB_DEVICE(USB_VENDOR_ID_UGEE, USB_DEVICE_ID_UGEE_TABLET_EX07S) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_HUION,
+				USB_DEVICE_ID_HUION_TABLET) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
+				USB_DEVICE_ID_HUION_TABLET) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
+				USB_DEVICE_ID_YIYNOVA_TABLET) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
+				USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_81) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
+				USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_45) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UCLOGIC,
+				USB_DEVICE_ID_UCLOGIC_DRAWIMAGE_G3) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UGTIZER,
+				USB_DEVICE_ID_UGTIZER_TABLET_GP0610) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_UGEE,
+				USB_DEVICE_ID_UGEE_TABLET_EX07S) },
 	{ }
 };
 MODULE_DEVICE_TABLE(hid, uclogic_devices);
@@ -481,6 +256,7 @@ static struct hid_driver uclogic_driver = {
 	.name = "uclogic",
 	.id_table = uclogic_devices,
 	.probe = uclogic_probe,
+	.remove = uclogic_remove,
 	.report_fixup = uclogic_report_fixup,
 	.raw_event = uclogic_raw_event,
 	.input_mapping = uclogic_input_mapping,
diff --git a/drivers/hid/hid-uclogic-params.c b/drivers/hid/hid-uclogic-params.c
new file mode 100644
index 000000000000..2f8870d58f9a
--- /dev/null
+++ b/drivers/hid/hid-uclogic-params.c
@@ -0,0 +1,806 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ *  HID driver for UC-Logic devices not fully compliant with HID standard
+ *  - tablet initialization and parameter retrieval
+ *
+ *  Copyright (c) 2018 Nikolai Kondrashov
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include "hid-uclogic-params.h"
+#include "hid-uclogic-rdesc.h"
+#include "usbhid/usbhid.h"
+#include "hid-ids.h"
+#include <linux/ctype.h>
+#include <asm/unaligned.h>
+
+/**
+ * Convert a pen in-range reporting type to a string.
+ *
+ * @inrange:	The in-range reporting type to convert.
+ *
+ * Returns:
+ *	The string representing the type, or NULL if the type is unknown.
+ */
+const char *uclogic_params_pen_inrange_to_str(
+			enum uclogic_params_pen_inrange inrange)
+{
+	switch (inrange) {
+	case UCLOGIC_PARAMS_PEN_INRANGE_NORMAL:
+		return "normal";
+	case UCLOGIC_PARAMS_PEN_INRANGE_INVERTED:
+		return "inverted";
+	default:
+		return NULL;
+	}
+}
+
+/**
+ * uclogic_params_get_str_desc - retrieve a string descriptor from a HID
+ * device interface, putting it into a kmalloc-allocated buffer as is, without
+ * character encoding conversion.
+ *
+ * @pbuf:	Location for the kmalloc-allocated buffer pointer containing
+ *		the retrieved descriptor. Not modified in case of error.
+ *		Can be NULL to have retrieved descriptor discarded.
+ * @hdev:	The HID device of the tablet interface to retrieve the string
+ *		descriptor from. Cannot be NULL.
+ * @idx:	Index of the string descriptor to request from the device.
+ * @len:	Length of the buffer to allocate and the data to retrieve.
+ *
+ * Returns:
+ *	number of bytes retrieved (<= len),
+ *	-EPIPE, if the descriptor was not found, or
+ *	another negative errno code in case of other error.
+ */
+static int uclogic_params_get_str_desc(__u8 **pbuf, struct hid_device *hdev,
+					__u8 idx, size_t len)
+{
+	int rc;
+	struct usb_device *udev = hid_to_usb_dev(hdev);
+	__u8 *buf = NULL;
+
+	/* Check arguments */
+	if (hdev == NULL) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (buf == NULL) {
+		rc = -ENOMEM;
+		goto cleanup;
+	}
+
+	rc = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
+				USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
+				(USB_DT_STRING << 8) + idx,
+				0x0409, buf, len,
+				USB_CTRL_GET_TIMEOUT);
+	if (rc == -EPIPE) {
+		hid_dbg(hdev, "string descriptor #%hhu not found\n", idx);
+		goto cleanup;
+	} else if (rc < 0) {
+		hid_err(hdev,
+			"failed retrieving string descriptor #%hhu: %d\n",
+			idx, rc);
+		goto cleanup;
+	}
+
+	if (pbuf != NULL) {
+		*pbuf = buf;
+		buf = NULL;
+	}
+
+cleanup:
+	kfree(buf);
+	return rc;
+}
+
+/**
+ * uclogic_params_pen_cleanup - free resources used by struct
+ * uclogic_params_pen (tablet interface's pen input parameters).
+ * Can be called repeatedly.
+ *
+ * @pen:	Pen input parameters to cleanup. Cannot be NULL.
+ */
+static void uclogic_params_pen_cleanup(struct uclogic_params_pen *pen)
+{
+	kfree(pen->desc_ptr);
+	memset(pen, 0, sizeof(*pen));
+}
+
+/**
+ * uclogic_params_pen_init() - initialize tablet interface pen
+ * input and retrieve its parameters from the device.
+ *
+ * @pen:	Pointer to the pen parameters to initialize (to be
+ *		cleaned up with uclogic_params_pen_cleanup()). Not modified in
+ *		case of error, or if parameters are not found. Cannot be NULL.
+ * @pfound:	Location for a flag which is set to true if the parameters
+ *		were found, and to false if not (e.g. device was
+ *		incompatible). Not modified in case of error. Cannot be NULL.
+ * @hdev:	The HID device of the tablet interface to initialize and get
+ *		parameters from. Cannot be NULL.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+static int uclogic_params_pen_init(struct uclogic_params_pen *pen,
+				   bool *pfound,
+				   struct hid_device *hdev)
+{
+	int rc;
+	bool found = false;
+	/* Buffer for (part of) the string descriptor */
+	__u8 *buf = NULL;
+	/* Minimum descriptor length required, maximum seen so far is 18 */
+	const int len = 12;
+	s32 resolution;
+	/* Pen report descriptor template parameters */
+	s32 desc_params[UCLOGIC_RDESC_PEN_PH_ID_NUM];
+	__u8 *desc_ptr = NULL;
+
+	/* Check arguments */
+	if (pen == NULL || pfound == NULL || hdev == NULL) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	/*
+	 * Read string descriptor containing pen input parameters.
+	 * The specific string descriptor and data were discovered by sniffing
+	 * the Windows driver traffic.
+	 * NOTE: This enables fully-functional tablet mode.
+	 */
+	rc = uclogic_params_get_str_desc(&buf, hdev, 100, len);
+	if (rc == -EPIPE) {
+		hid_dbg(hdev,
+			"string descriptor with pen parameters not found, assuming not compatible\n");
+		goto finish;
+	} else if (rc < 0) {
+		hid_err(hdev, "failed retrieving pen parameters: %d\n", rc);
+		goto cleanup;
+	} else if (rc != len) {
+		hid_dbg(hdev,
+			"string descriptor with pen parameters has invalid length (got %d, expected %d), assuming not compatible\n",
+			rc, len);
+		goto finish;
+	}
+
+	/*
+	 * Fill report descriptor parameters from the string descriptor
+	 */
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] =
+		get_unaligned_le16(buf + 2);
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] =
+		get_unaligned_le16(buf + 4);
+	desc_params[UCLOGIC_RDESC_PEN_PH_ID_PRESSURE_LM] =
+		get_unaligned_le16(buf + 8);
+	resolution = get_unaligned_le16(buf + 10);
+	if (resolution == 0) {
+		desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] = 0;
+		desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] = 0;
+	} else {
+		desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_PM] =
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_X_LM] * 1000 /
+			resolution;
+		desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_PM] =
+			desc_params[UCLOGIC_RDESC_PEN_PH_ID_Y_LM] * 1000 /
+			resolution;
+	}
+	kfree(buf);
+	buf = NULL;
+
+	/*
+	 * Generate pen report descriptor
+	 */
+	desc_ptr = uclogic_rdesc_template_apply(
+				uclogic_rdesc_pen_template_arr,
+				uclogic_rdesc_pen_template_size,
+				desc_params, ARRAY_SIZE(desc_params));
+	if (desc_ptr == NULL) {
+		rc = -ENOMEM;
+		goto cleanup;
+	}
+
+	/*
+	 * Fill-in the parameters
+	 */
+	memset(pen, 0, sizeof(*pen));
+	pen->desc_ptr = desc_ptr;
+	desc_ptr = NULL;
+	pen->desc_size = uclogic_rdesc_pen_template_size;
+	pen->id = UCLOGIC_RDESC_PEN_ID;
+	pen->inrange = UCLOGIC_PARAMS_PEN_INRANGE_INVERTED;
+	found = true;
+finish:
+	*pfound = found;
+	rc = 0;
+cleanup:
+	kfree(desc_ptr);
+	kfree(buf);
+	return rc;
+}
+
+/**
+ * uclogic_params_frame_cleanup - free resources used by struct
+ * uclogic_params_frame (tablet interface's frame controls input parameters).
+ * Can be called repeatedly.
+ *
+ * @frame:	Frame controls input parameters to cleanup. Cannot be NULL.
+ */
+static void uclogic_params_frame_cleanup(struct uclogic_params_frame *frame)
+{
+	kfree(frame->desc_ptr);
+	memset(frame, 0, sizeof(*frame));
+}
+
+/**
+ * uclogic_params_frame_init_with_desc() - initialize tablet's frame control
+ * parameters with a static report descriptor.
+ *
+ * @frame:	Pointer to the frame parameters to initialize (to be cleaned
+ *		up with uclogic_params_frame_cleanup()). Not modified in case
+ *		of error. Cannot be NULL.
+ * @desc_ptr:	Report descriptor pointer. Can be NULL, if desc_size is zero.
+ * @desc_size:	Report descriptor size.
+ * @id:		Report ID used for frame reports, if they should be tweaked,
+ *		zero if not.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+static int uclogic_params_frame_init_with_desc(
+					struct uclogic_params_frame *frame,
+					const __u8 *desc_ptr,
+					size_t desc_size,
+					unsigned int id)
+{
+	__u8 *copy_desc_ptr;
+
+	if (frame == NULL || (desc_ptr == NULL && desc_size != 0))
+		return -EINVAL;
+
+	copy_desc_ptr = kmemdup(desc_ptr, desc_size, GFP_KERNEL);
+	if (copy_desc_ptr == NULL)
+		return -ENOMEM;
+
+	memset(frame, 0, sizeof(*frame));
+	frame->desc_ptr = copy_desc_ptr;
+	frame->desc_size = desc_size;
+	frame->id = id;
+	return 0;
+}
+
+/**
+ * uclogic_params_frame_init_buttonpad() - initialize abstract buttonpad
+ * on a tablet interface.
+ *
+ * @frame:	Pointer to the frame parameters to initialize (to be cleaned
+ *		up with uclogic_params_frame_cleanup()). Not modified in case
+ *		of error, or if parameters are not found. Cannot be NULL.
+ * @pfound:	Location for a flag which is set to true if the parameters
+ *		were found, and to false if not (e.g. device was
+ *		incompatible). Not modified in case of error. Cannot be NULL.
+ * @hdev:	The HID device of the tablet interface to initialize and get
+ *		parameters from. Cannot be NULL.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+static int uclogic_params_frame_init_buttonpad(
+					struct uclogic_params_frame *frame,
+					bool *pfound,
+					struct hid_device *hdev)
+{
+	int rc;
+	bool found = false;
+	struct usb_device *usb_dev = hid_to_usb_dev(hdev);
+	char *str_buf = NULL;
+	const size_t str_len = 16;
+
+	/* Check arguments */
+	if (frame == NULL || pfound == NULL || hdev == NULL) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	/*
+	 * Enable generic button mode
+	 */
+	str_buf = kzalloc(str_len, GFP_KERNEL);
+	if (str_buf == NULL) {
+		rc = -ENOMEM;
+		goto cleanup;
+	}
+
+	rc = usb_string(usb_dev, 123, str_buf, str_len);
+	if (rc == -EPIPE) {
+		hid_dbg(hdev,
+			"generic button -enabling string descriptor not found\n");
+	} else if (rc < 0) {
+		goto cleanup;
+	} else if (strncmp(str_buf, "HK On", rc) != 0) {
+		hid_dbg(hdev,
+			"invalid response to enabling generic buttons: \"%s\"\n",
+			str_buf);
+	} else {
+		hid_dbg(hdev, "generic buttons enabled\n");
+		rc = uclogic_params_frame_init_with_desc(
+				frame,
+				uclogic_rdesc_buttonpad_arr,
+				uclogic_rdesc_buttonpad_size,
+				UCLOGIC_RDESC_BUTTONPAD_ID);
+		if (rc != 0)
+			goto cleanup;
+		found = true;
+	}
+
+	*pfound = found;
+	rc = 0;
+cleanup:
+	kfree(str_buf);
+	return rc;
+}
+
+/**
+ * uclogic_params_cleanup - free resources used by struct uclogic_params
+ * (tablet interface's parameters).
+ * Can be called repeatedly.
+ *
+ * @params:	Input parameters to cleanup. Cannot be NULL.
+ */
+void uclogic_params_cleanup(struct uclogic_params *params)
+{
+	if (!params->invalid) {
+		kfree(params->desc_ptr);
+		if (!params->pen_unused)
+			uclogic_params_pen_cleanup(&params->pen);
+		uclogic_params_frame_cleanup(&params->frame);
+		memset(params, 0, sizeof(*params));
+	}
+}
+
+/**
+ * Get a replacement report descriptor for a tablet's interface.
+ *
+ * @params:	The parameters of a tablet interface to get report
+ *		descriptor for. Cannot be NULL.
+ * @pdesc:	Location for the resulting, kmalloc-allocated report
+ *		descriptor pointer, or for NULL, if there's no replacement
+ *		report descriptor. Not modified in case of error. Cannot be
+ *		NULL.
+ * @psize:	Location for the resulting report descriptor size, not set if
+ *		there's no replacement report descriptor. Not modified in case
+ *		of error. Cannot be NULL.
+ *
+ * Returns:
+ *	Zero, if successful.
+ *	-EINVAL, if invalid arguments are supplied.
+ *	-ENOMEM, if failed to allocate memory.
+ */
+int uclogic_params_get_desc(const struct uclogic_params *params,
+				__u8 **pdesc,
+				unsigned int *psize)
+{
+	bool common_present;
+	bool pen_present;
+	bool frame_present;
+	unsigned int size;
+	__u8 *desc = NULL;
+
+	/* Check arguments */
+	if (params == NULL || pdesc == NULL || psize == NULL)
+		return -EINVAL;
+
+	size = 0;
+
+	common_present = (params->desc_ptr != NULL);
+	pen_present = (!params->pen_unused && params->pen.desc_ptr != NULL);
+	frame_present = (params->frame.desc_ptr != NULL);
+
+	if (common_present)
+		size += params->desc_size;
+	if (pen_present)
+		size += params->pen.desc_size;
+	if (frame_present)
+		size += params->frame.desc_size;
+
+	if (common_present || pen_present || frame_present) {
+		__u8 *p;
+
+		desc = kmalloc(size, GFP_KERNEL);
+		if (desc == NULL)
+			return -ENOMEM;
+		p = desc;
+
+		if (common_present) {
+			memcpy(p, params->desc_ptr,
+				params->desc_size);
+			p += params->desc_size;
+		}
+		if (pen_present) {
+			memcpy(p, params->pen.desc_ptr,
+				params->pen.desc_size);
+			p += params->pen.desc_size;
+		}
+		if (frame_present) {
+			memcpy(p, params->frame.desc_ptr,
+				params->frame.desc_size);
+			p += params->frame.desc_size;
+		}
+
+		WARN_ON(p != desc + size);
+
+		*psize = size;
+	}
+
+	*pdesc = desc;
+	return 0;
+}
+
+/**
+ * uclogic_params_init_invalid() - initialize tablet interface parameters,
+ * specifying the interface is invalid.
+ *
+ * @params:		Parameters to initialize (to be cleaned with
+ *			uclogic_params_cleanup()). Cannot be NULL.
+ */
+static void uclogic_params_init_invalid(struct uclogic_params *params)
+{
+	params->invalid = true;
+}
+
+/**
+ * uclogic_params_init_with_opt_desc() - initialize tablet interface
+ * parameters with an optional replacement report descriptor. Only modify
+ * report descriptor, if the original report descriptor matches the expected
+ * size.
+ *
+ * @params:		Parameters to initialize (to be cleaned with
+ *			uclogic_params_cleanup()). Not modified in case of
+ *			error. Cannot be NULL.
+ * @hdev:		The HID device of the tablet interface create the
+ *			parameters for. Cannot be NULL.
+ * @orig_desc_size:	Expected size of the original report descriptor to
+ *			be replaced.
+ * @desc_ptr:		Pointer to the replacement report descriptor.
+ *			Can be NULL, if desc_size is zero.
+ * @desc_size:		Size of the replacement report descriptor.
+ *
+ * Returns:
+ *	Zero, if successful. -EINVAL if an invalid argument was passed.
+ *	-ENOMEM, if failed to allocate memory.
+ */
+static int uclogic_params_init_with_opt_desc(struct uclogic_params *params,
+					     struct hid_device *hdev,
+					     unsigned int orig_desc_size,
+					     __u8 *desc_ptr,
+					     unsigned int desc_size)
+{
+	__u8 *desc_copy_ptr = NULL;
+	unsigned int desc_copy_size;
+	int rc;
+
+	/* Check arguments */
+	if (params == NULL || hdev == NULL ||
+	    (desc_ptr == NULL && desc_size != 0)) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	/* Replace report descriptor, if it matches */
+	if (hdev->dev_rsize == orig_desc_size) {
+		hid_dbg(hdev,
+			"device report descriptor matches the expected size, replacing\n");
+		desc_copy_ptr = kmemdup(desc_ptr, desc_size, GFP_KERNEL);
+		if (desc_copy_ptr == NULL) {
+			rc = -ENOMEM;
+			goto cleanup;
+		}
+		desc_copy_size = desc_size;
+	} else {
+		hid_dbg(hdev,
+			"device report descriptor doesn't match the expected size (%u != %u), preserving\n",
+			hdev->dev_rsize, orig_desc_size);
+		desc_copy_ptr = NULL;
+		desc_copy_size = 0;
+	}
+
+	/* Output parameters */
+	memset(params, 0, sizeof(*params));
+	params->desc_ptr = desc_copy_ptr;
+	desc_copy_ptr = NULL;
+	params->desc_size = desc_copy_size;
+
+	rc = 0;
+cleanup:
+	kfree(desc_copy_ptr);
+	return rc;
+}
+
+/**
+ * uclogic_params_init_with_pen_unused() - initialize tablet interface
+ * parameters preserving original reports and generic HID processing, but
+ * disabling pen usage.
+ *
+ * @params:		Parameters to initialize (to be cleaned with
+ *			uclogic_params_cleanup()). Not modified in case of
+ *			error. Cannot be NULL.
+ */
+static void uclogic_params_init_with_pen_unused(struct uclogic_params *params)
+{
+	memset(params, 0, sizeof(*params));
+	params->pen_unused = true;
+}
+
+/**
+ * uclogic_params_init() - initialize a Huion tablet interface and discover
+ * its parameters.
+ *
+ * @params:	Parameters to fill in (to be cleaned with
+ *		uclogic_params_cleanup()). Not modified in case of error.
+ *		Cannot be NULL.
+ * @hdev:	The HID device of the tablet interface to initialize and get
+ *		parameters from. Cannot be NULL.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+static int uclogic_params_huion_init(struct uclogic_params *params,
+				     struct hid_device *hdev)
+{
+	int rc;
+	struct usb_interface *iface = to_usb_interface(hdev->dev.parent);
+	__u8 bInterfaceNumber = iface->cur_altsetting->desc.bInterfaceNumber;
+	bool found;
+	/* The resulting parameters (noop) */
+	struct uclogic_params p = {0, };
+
+	/* Check arguments */
+	if (params == NULL || hdev == NULL) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	/* If it's not a pen interface */
+	if (bInterfaceNumber != 0) {
+		/* TODO: Consider marking the interface invalid */
+		uclogic_params_init_with_pen_unused(&p);
+		goto output;
+	}
+
+	/* Try to probe pen parameters */
+	rc = uclogic_params_pen_init(&p.pen, &found, hdev);
+	if (rc != 0) {
+		hid_err(hdev,
+			"failed probing pen parameters: %d\n", rc);
+		goto cleanup;
+	} else if (found) {
+		hid_dbg(hdev, "pen parameters found\n");
+		/* Try to probe buttonpad */
+		rc = uclogic_params_frame_init_buttonpad(
+						&p.frame,
+						&found, hdev);
+		if (rc != 0) {
+			hid_err(hdev, "v1 buttonpad probing failed: %d\n", rc);
+			goto cleanup;
+		}
+		hid_dbg(hdev, "buttonpad parameters%s found\n",
+			(found ? "" : " not"));
+		if (found) {
+			/* Set bitmask marking frame reports */
+			p.pen_frame_flag = 0x20;
+		}
+		goto output;
+	}
+	hid_dbg(hdev, "pen parameters not found\n");
+
+	uclogic_params_init_invalid(&p);
+
+output:
+	/* Output parameters */
+	memcpy(params, &p, sizeof(*params));
+	memset(&p, 0, sizeof(p));
+	rc = 0;
+cleanup:
+	uclogic_params_cleanup(&p);
+	return rc;
+}
+
+/**
+ * uclogic_params_init() - initialize a tablet interface and discover its
+ * parameters.
+ *
+ * @params:	Parameters to fill in (to be cleaned with
+ *		uclogic_params_cleanup()). Not modified in case of error.
+ *		Cannot be NULL.
+ * @hdev:	The HID device of the tablet interface to initialize and get
+ *		parameters from. Cannot be NULL.
+ *
+ * Returns:
+ *	Zero, if successful. A negative errno code on error.
+ */
+int uclogic_params_init(struct uclogic_params *params,
+			struct hid_device *hdev)
+{
+	int rc;
+	struct usb_device *udev = hid_to_usb_dev(hdev);
+	__u8  bNumInterfaces = udev->config->desc.bNumInterfaces;
+	struct usb_interface *iface = to_usb_interface(hdev->dev.parent);
+	__u8 bInterfaceNumber = iface->cur_altsetting->desc.bInterfaceNumber;
+	bool found;
+	/* The resulting parameters (noop) */
+	struct uclogic_params p = {0, };
+
+	/* Check arguments */
+	if (params == NULL || hdev == NULL) {
+		rc = -EINVAL;
+		goto cleanup;
+	}
+
+	/*
+	 * Set replacement report descriptor if the original matches the
+	 * specified size. Otherwise keep interface unchanged.
+	 */
+#define WITH_OPT_DESC(_orig_desc_token, _new_desc_token) \
+	uclogic_params_init_with_opt_desc(                  \
+		&p, hdev,                                   \
+		UCLOGIC_RDESC_##_orig_desc_token##_SIZE,    \
+		uclogic_rdesc_##_new_desc_token##_arr,      \
+		uclogic_rdesc_##_new_desc_token##_size)
+
+#define VID_PID(_vid, _pid) \
+	(((__u32)(_vid) << 16) | ((__u32)(_pid) & U16_MAX))
+
+	/*
+	 * Handle specific interfaces for specific tablets.
+	 *
+	 * Observe the following logic:
+	 *
+	 * If the interface is recognized as producing certain useful input:
+	 *	Mark interface as valid.
+	 *	Output interface parameters.
+	 * Else, if the interface is recognized as *not* producing any useful
+	 * input:
+	 *	Mark interface as invalid.
+	 * Else:
+	 *	Mark interface as valid.
+	 *	Output noop parameters.
+	 *
+	 * Rule of thumb: it is better to disable a broken interface than let
+	 *		  it spew garbage input.
+	 */
+
+	switch (VID_PID(hdev->vendor, hdev->product)) {
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_PF1209):
+		rc = WITH_OPT_DESC(PF1209_ORIG, pf1209_fixed);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_WP4030U):
+		rc = WITH_OPT_DESC(WPXXXXU_ORIG, wp4030u_fixed);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_WP5540U):
+		rc = WITH_OPT_DESC(WPXXXXU_ORIG, wp5540u_fixed);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_WP8060U):
+		rc = WITH_OPT_DESC(WPXXXXU_ORIG, wp8060u_fixed);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_WP1062):
+		rc = WITH_OPT_DESC(WP1062_ORIG, wp1062_fixed);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_WIRELESS_TABLET_TWHL850):
+		switch (bInterfaceNumber) {
+		case 0:
+			rc = WITH_OPT_DESC(TWHL850_ORIG0, twhl850_fixed0);
+			if (rc != 0)
+				goto cleanup;
+			break;
+		case 1:
+			rc = WITH_OPT_DESC(TWHL850_ORIG1, twhl850_fixed1);
+			if (rc != 0)
+				goto cleanup;
+			break;
+		case 2:
+			rc = WITH_OPT_DESC(TWHL850_ORIG2, twhl850_fixed2);
+			if (rc != 0)
+				goto cleanup;
+			break;
+		}
+		break;
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_TABLET_TWHA60):
+		/*
+		 * If it is not a three-interface version, which is known to
+		 * respond to initialization.
+		 */
+		if (bNumInterfaces != 3) {
+			switch (bInterfaceNumber) {
+			case 0:
+				rc = WITH_OPT_DESC(TWHA60_ORIG0,
+							twha60_fixed0);
+				if (rc != 0)
+					goto cleanup;
+				break;
+			case 1:
+				rc = WITH_OPT_DESC(TWHA60_ORIG1,
+							twha60_fixed1);
+				if (rc != 0)
+					goto cleanup;
+				break;
+			}
+			break;
+		}
+		/* FALL THROUGH */
+	case VID_PID(USB_VENDOR_ID_HUION,
+		     USB_DEVICE_ID_HUION_TABLET):
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_HUION_TABLET):
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_YIYNOVA_TABLET):
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_81):
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_DRAWIMAGE_G3):
+	case VID_PID(USB_VENDOR_ID_UCLOGIC,
+		     USB_DEVICE_ID_UCLOGIC_UGEE_TABLET_45):
+		rc = uclogic_params_huion_init(&p, hdev);
+		if (rc != 0)
+			goto cleanup;
+		break;
+	case VID_PID(USB_VENDOR_ID_UGTIZER,
+		     USB_DEVICE_ID_UGTIZER_TABLET_GP0610):
+	case VID_PID(USB_VENDOR_ID_UGEE,
+		     USB_DEVICE_ID_UGEE_TABLET_EX07S):
+		/* If this is the pen interface */
+		if (bInterfaceNumber == 1) {
+			/* Probe pen parameters */
+			rc = uclogic_params_pen_init(&p.pen, &found, hdev);
+			if (rc != 0) {
+				hid_err(hdev, "pen probing failed: %d\n", rc);
+				goto cleanup;
+			}
+			if (!found) {
+				hid_warn(hdev, "pen parameters not found");
+				uclogic_params_init_invalid(&p);
+			}
+		} else {
+			/* TODO: Consider marking the interface invalid */
+			uclogic_params_init_with_pen_unused(&p);
+		}
+		break;
+	}
+
+#undef VID_PID
+#undef WITH_OPT_DESC
+
+	/* Output parameters */
+	memcpy(params, &p, sizeof(*params));
+	memset(&p, 0, sizeof(p));
+	rc = 0;
+cleanup:
+	uclogic_params_cleanup(&p);
+	return rc;
+}
diff --git a/drivers/hid/hid-uclogic-params.h b/drivers/hid/hid-uclogic-params.h
new file mode 100644
index 000000000000..4c78d9dd0576
--- /dev/null
+++ b/drivers/hid/hid-uclogic-params.h
@@ -0,0 +1,180 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ *  HID driver for UC-Logic devices not fully compliant with HID standard
+ *  - tablet initialization and parameter retrieval
+ *
+ *  Copyright (c) 2018 Nikolai Kondrashov
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#ifndef _HID_UCLOGIC_PARAMS_H
+#define _HID_UCLOGIC_PARAMS_H
+
+#include <linux/usb.h>
+#include <linux/hid.h>
+
+/* Types of pen in-range reporting */
+enum uclogic_params_pen_inrange {
+	/* Normal reports: zero - out of proximity, one - in proximity */
+	UCLOGIC_PARAMS_PEN_INRANGE_NORMAL = 0,
+	/* Inverted reports: zero - in proximity, one - out of proximity */
+	UCLOGIC_PARAMS_PEN_INRANGE_INVERTED,
+};
+
+/* Convert a pen in-range reporting type to a string */
+extern const char *uclogic_params_pen_inrange_to_str(
+			enum uclogic_params_pen_inrange inrange);
+
+/*
+ * Tablet interface's pen input parameters.
+ *
+ * Must use declarative (descriptive) language, not imperative, to simplify
+ * understanding and maintain consistency.
+ *
+ * Noop (preserving functionality) when filled with zeroes.
+ */
+struct uclogic_params_pen {
+	/*
+	 * Pointer to report descriptor describing the inputs.
+	 * Allocated with kmalloc.
+	 */
+	__u8 *desc_ptr;
+	/*
+	 * Size of the report descriptor.
+	 * Only valid, if "desc_ptr" is not NULL.
+	 */
+	unsigned int desc_size;
+	/* Report ID, if reports should be tweaked, zero if not */
+	unsigned int id;
+	/* Type of in-range reporting, only valid if "id" is not zero */
+	enum uclogic_params_pen_inrange inrange;
+};
+
+/*
+ * Parameters of frame control inputs of a tablet interface.
+ *
+ * Must use declarative (descriptive) language, not imperative, to simplify
+ * understanding and maintain consistency.
+ *
+ * Noop (preserving functionality) when filled with zeroes.
+ */
+struct uclogic_params_frame {
+	/*
+	 * Pointer to report descriptor describing the inputs.
+	 * Allocated with kmalloc.
+	 */
+	__u8 *desc_ptr;
+	/*
+	 * Size of the report descriptor.
+	 * Only valid, if "desc_ptr" is not NULL.
+	 */
+	unsigned int desc_size;
+	/*
+	 * Report ID, if reports should be tweaked, zero if not.
+	 */
+	unsigned int id;
+};
+
+/*
+ * Tablet interface report parameters.
+ *
+ * Must use declarative (descriptive) language, not imperative, to simplify
+ * understanding and maintain consistency.
+ *
+ * When filled with zeros represents a "noop" configuration - passes all
+ * reports unchanged and lets the generic HID driver handle everything.
+ *
+ * The resulting device report descriptor is assembled from all the report
+ * descriptor parts referenced by the structure. No order of assembly should
+ * be assumed. The structure represents original device report descriptor if
+ * all the parts are NULL.
+ */
+struct uclogic_params {
+	/*
+	 * True if the whole interface is invalid, false otherwise.
+	 */
+	bool invalid;
+	/*
+	 * Pointer to the common part of the replacement report descriptor,
+	 * allocated with kmalloc. NULL if no common part is needed.
+	 * Only valid, if "invalid" is false.
+	 */
+	__u8 *desc_ptr;
+	/*
+	 * Size of the common part of the replacement report descriptor.
+	 * Only valid, if "desc_ptr" is not NULL.
+	 */
+	unsigned int desc_size;
+	/*
+	 * True, if pen usage in report descriptor is invalid, when present.
+	 * Only valid, if "invalid" is false.
+	 */
+	bool pen_unused;
+	/*
+	 * Pen parameters and optional report descriptor part.
+	 * Only valid if "pen_unused" is valid and false.
+	 */
+	struct uclogic_params_pen pen;
+	/*
+	 * Frame control parameters and optional report descriptor part.
+	 * Only valid, if "invalid" is false.
+	 */
+	struct uclogic_params_frame frame;
+	/*
+	 * Bitmask matching frame controls "sub-report" flag in the second
+	 * byte of the pen report, or zero if it's not expected.
+	 * Only valid if both "pen" and "frame" are valid, and "frame.id" is
+	 * not zero.
+	 */
+	__u8 pen_frame_flag;
+};
+
+/* Initialize a tablet interface and discover its parameters */
+extern int uclogic_params_init(struct uclogic_params *params,
+				struct hid_device *hdev);
+
+/* Tablet interface parameters *printf format string */
+#define UCLOGIC_PARAMS_FMT_STR \
+		".invalid = %s\n"                   \
+		".desc_ptr = %p\n"                  \
+		".desc_size = %u\n"                 \
+		".pen_unused = %s\n"                \
+		".pen.desc_ptr = %p\n"              \
+		".pen.desc_size = %u\n"             \
+		".pen.id = %u\n"                    \
+		".pen.inrange = %s\n"               \
+		".frame.desc_ptr = %p\n"            \
+		".frame.desc_size = %u\n"           \
+		".frame.id = %u\n"                  \
+		".pen_frame_flag = 0x%02x\n"
+
+/* Tablet interface parameters *printf format arguments */
+#define UCLOGIC_PARAMS_FMT_ARGS(_params) \
+		((_params)->invalid ? "true" : "false"),                    \
+		(_params)->desc_ptr,                                        \
+		(_params)->desc_size,                                       \
+		((_params)->pen_unused ? "true" : "false"),                 \
+		(_params)->pen.desc_ptr,                                    \
+		(_params)->pen.desc_size,                                   \
+		(_params)->pen.id,                                          \
+		uclogic_params_pen_inrange_to_str((_params)->pen.inrange),  \
+		(_params)->frame.desc_ptr,                                  \
+		(_params)->frame.desc_size,                                 \
+		(_params)->frame.id,                                        \
+		(_params)->pen_frame_flag
+
+/* Get a replacement report descriptor for a tablet's interface. */
+extern int uclogic_params_get_desc(const struct uclogic_params *params,
+					__u8 **pdesc,
+					unsigned int *psize);
+
+/* Free resources used by tablet interface's parameters */
+extern void uclogic_params_cleanup(struct uclogic_params *params);
+
+#endif /* _HID_UCLOGIC_PARAMS_H */