drm: Split out drm_probe_helper.c from drm_crtc_helper.c

This is leftover stuff from my previous doc round which I kinda wanted
to do but didn't yet due to rebase hell.

The modeset helpers and the probing helpers a independent and e.g.
i915 uses the probing stuff but has its own modeset infrastructure. It
hence makes to split this up. While at it add a DOC: comment for the
probing libraray.

It would be rather neat to pull some of the DocBook documenting these
two helpers into in-line DOC: comments. But unfortunately kerneldoc
doesn't support markdown or something similar to make nice-looking
documentation, so the current state is better.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

3 files changed, 427 insertions, 371 deletions

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 9d25dbbe6771..48e38ba22783 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -23,7 +23,7 @@ drm-$(CONFIG_DRM_PANEL) += drm_panel.o
 
 drm-usb-y   := drm_usb.o
 
-drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o
+drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o
 drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 drm_kms_helper-$(CONFIG_DRM_KMS_FB_HELPER) += drm_fb_helper.o
 drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index c43825e8f5c1..df281b54db01 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -72,147 +72,6 @@ void drm_helper_move_panel_connectors_to_head(struct drm_device *dev)
 }
 EXPORT_SYMBOL(drm_helper_move_panel_connectors_to_head);
 
-static bool drm_kms_helper_poll = true;
-module_param_named(poll, drm_kms_helper_poll, bool, 0600);
-
-static void drm_mode_validate_flag(struct drm_connector *connector,
-				   int flags)
-{
-	struct drm_display_mode *mode;
-
-	if (flags == (DRM_MODE_FLAG_DBLSCAN | DRM_MODE_FLAG_INTERLACE |
-		      DRM_MODE_FLAG_3D_MASK))
-		return;
-
-	list_for_each_entry(mode, &connector->modes, head) {
-		if ((mode->flags & DRM_MODE_FLAG_INTERLACE) &&
-				!(flags & DRM_MODE_FLAG_INTERLACE))
-			mode->status = MODE_NO_INTERLACE;
-		if ((mode->flags & DRM_MODE_FLAG_DBLSCAN) &&
-				!(flags & DRM_MODE_FLAG_DBLSCAN))
-			mode->status = MODE_NO_DBLESCAN;
-		if ((mode->flags & DRM_MODE_FLAG_3D_MASK) &&
-				!(flags & DRM_MODE_FLAG_3D_MASK))
-			mode->status = MODE_NO_STEREO;
-	}
-
-	return;
-}
-
-/**
- * drm_helper_probe_single_connector_modes - get complete set of display modes
- * @connector: connector to probe
- * @maxX: max width for modes
- * @maxY: max height for modes
- *
- * Based on the helper callbacks implemented by @connector try to detect all
- * valid modes.  Modes will first be added to the connector's probed_modes list,
- * then culled (based on validity and the @maxX, @maxY parameters) and put into
- * the normal modes list.
- *
- * Intended to be use as a generic implementation of the ->fill_modes()
- * @connector vfunc for drivers that use the crtc helpers for output mode
- * filtering and detection.
- *
- * Returns:
- * The number of modes found on @connector.
- */
-int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
-					    uint32_t maxX, uint32_t maxY)
-{
-	struct drm_device *dev = connector->dev;
-	struct drm_display_mode *mode;
-	struct drm_connector_helper_funcs *connector_funcs =
-		connector->helper_private;
-	int count = 0;
-	int mode_flags = 0;
-	bool verbose_prune = true;
-
-	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
-
-	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
-			drm_get_connector_name(connector));
-	/* set all modes to the unverified state */
-	list_for_each_entry(mode, &connector->modes, head)
-		mode->status = MODE_UNVERIFIED;
-
-	if (connector->force) {
-		if (connector->force == DRM_FORCE_ON)
-			connector->status = connector_status_connected;
-		else
-			connector->status = connector_status_disconnected;
-		if (connector->funcs->force)
-			connector->funcs->force(connector);
-	} else {
-		connector->status = connector->funcs->detect(connector, true);
-	}
-
-	/* Re-enable polling in case the global poll config changed. */
-	if (drm_kms_helper_poll != dev->mode_config.poll_running)
-		drm_kms_helper_poll_enable(dev);
-
-	dev->mode_config.poll_running = drm_kms_helper_poll;
-
-	if (connector->status == connector_status_disconnected) {
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
-			connector->base.id, drm_get_connector_name(connector));
-		drm_mode_connector_update_edid_property(connector, NULL);
-		verbose_prune = false;
-		goto prune;
-	}
-
-#ifdef CONFIG_DRM_LOAD_EDID_FIRMWARE
-	count = drm_load_edid_firmware(connector);
-	if (count == 0)
-#endif
-		count = (*connector_funcs->get_modes)(connector);
-
-	if (count == 0 && connector->status == connector_status_connected)
-		count = drm_add_modes_noedid(connector, 1024, 768);
-	if (count == 0)
-		goto prune;
-
-	drm_mode_connector_list_update(connector);
-
-	if (maxX && maxY)
-		drm_mode_validate_size(dev, &connector->modes, maxX, maxY);
-
-	if (connector->interlace_allowed)
-		mode_flags |= DRM_MODE_FLAG_INTERLACE;
-	if (connector->doublescan_allowed)
-		mode_flags |= DRM_MODE_FLAG_DBLSCAN;
-	if (connector->stereo_allowed)
-		mode_flags |= DRM_MODE_FLAG_3D_MASK;
-	drm_mode_validate_flag(connector, mode_flags);
-
-	list_for_each_entry(mode, &connector->modes, head) {
-		if (mode->status == MODE_OK)
-			mode->status = connector_funcs->mode_valid(connector,
-								   mode);
-	}
-
-prune:
-	drm_mode_prune_invalid(dev, &connector->modes, verbose_prune);
-
-	if (list_empty(&connector->modes))
-		return 0;
-
-	list_for_each_entry(mode, &connector->modes, head)
-		mode->vrefresh = drm_mode_vrefresh(mode);
-
-	drm_mode_sort(&connector->modes);
-
-	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] probed modes :\n", connector->base.id,
-			drm_get_connector_name(connector));
-	list_for_each_entry(mode, &connector->modes, head) {
-		drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
-		drm_mode_debug_printmodeline(mode);
-	}
-
-	return count;
-}
-EXPORT_SYMBOL(drm_helper_probe_single_connector_modes);
-
 /**
  * drm_helper_encoder_in_use - check if a given encoder is in use
  * @encoder: encoder to check
@@ -1020,232 +879,3 @@ void drm_helper_resume_force_mode(struct drm_device *dev)
 	drm_modeset_unlock_all(dev);
 }
 EXPORT_SYMBOL(drm_helper_resume_force_mode);
-
-/**
- * drm_kms_helper_hotplug_event - fire off KMS hotplug events
- * @dev: drm_device whose connector state changed
- *
- * This function fires off the uevent for userspace and also calls the
- * output_poll_changed function, which is most commonly used to inform the fbdev
- * emulation code and allow it to update the fbcon output configuration.
- *
- * Drivers should call this from their hotplug handling code when a change is
- * detected. Note that this function does not do any output detection of its
- * own, like drm_helper_hpd_irq_event() does - this is assumed to be done by the
- * driver already.
- *
- * This function must be called from process context with no mode
- * setting locks held.
- */
-void drm_kms_helper_hotplug_event(struct drm_device *dev)
-{
-	/* send a uevent + call fbdev */
-	drm_sysfs_hotplug_event(dev);
-	if (dev->mode_config.funcs->output_poll_changed)
-		dev->mode_config.funcs->output_poll_changed(dev);
-}
-EXPORT_SYMBOL(drm_kms_helper_hotplug_event);
-
-#define DRM_OUTPUT_POLL_PERIOD (10*HZ)
-static void output_poll_execute(struct work_struct *work)
-{
-	struct delayed_work *delayed_work = to_delayed_work(work);
-	struct drm_device *dev = container_of(delayed_work, struct drm_device, mode_config.output_poll_work);
-	struct drm_connector *connector;
-	enum drm_connector_status old_status;
-	bool repoll = false, changed = false;
-
-	if (!drm_kms_helper_poll)
-		return;
-
-	mutex_lock(&dev->mode_config.mutex);
-	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
-
-		/* Ignore forced connectors. */
-		if (connector->force)
-			continue;
-
-		/* Ignore HPD capable connectors and connectors where we don't
-		 * want any hotplug detection at all for polling. */
-		if (!connector->polled || connector->polled == DRM_CONNECTOR_POLL_HPD)
-			continue;
-
-		repoll = true;
-
-		old_status = connector->status;
-		/* if we are connected and don't want to poll for disconnect
-		   skip it */
-		if (old_status == connector_status_connected &&
-		    !(connector->polled & DRM_CONNECTOR_POLL_DISCONNECT))
-			continue;
-
-		connector->status = connector->funcs->detect(connector, false);
-		if (old_status != connector->status) {
-			const char *old, *new;
-
-			old = drm_get_connector_status_name(old_status);
-			new = drm_get_connector_status_name(connector->status);
-
-			DRM_DEBUG_KMS("[CONNECTOR:%d:%s] "
-				      "status updated from %s to %s\n",
-				      connector->base.id,
-				      drm_get_connector_name(connector),
-				      old, new);
-
-			changed = true;
-		}
-	}
-
-	mutex_unlock(&dev->mode_config.mutex);
-
-	if (changed)
-		drm_kms_helper_hotplug_event(dev);
-
-	if (repoll)
-		schedule_delayed_work(delayed_work, DRM_OUTPUT_POLL_PERIOD);
-}
-
-/**
- * drm_kms_helper_poll_disable - disable output polling
- * @dev: drm_device
- *
- * This function disables the output polling work.
- *
- * Drivers can call this helper from their device suspend implementation. It is
- * not an error to call this even when output polling isn't enabled or arlready
- * disabled.
- */
-void drm_kms_helper_poll_disable(struct drm_device *dev)
-{
-	if (!dev->mode_config.poll_enabled)
-		return;
-	cancel_delayed_work_sync(&dev->mode_config.output_poll_work);
-}
-EXPORT_SYMBOL(drm_kms_helper_poll_disable);
-
-/**
- * drm_kms_helper_poll_enable - re-enable output polling.
- * @dev: drm_device
- *
- * This function re-enables the output polling work.
- *
- * Drivers can call this helper from their device resume implementation. It is
- * an error to call this when the output polling support has not yet been set
- * up.
- */
-void drm_kms_helper_poll_enable(struct drm_device *dev)
-{
-	bool poll = false;
-	struct drm_connector *connector;
-
-	if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll)
-		return;
-
-	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
-		if (connector->polled & (DRM_CONNECTOR_POLL_CONNECT |
-					 DRM_CONNECTOR_POLL_DISCONNECT))
-			poll = true;
-	}
-
-	if (poll)
-		schedule_delayed_work(&dev->mode_config.output_poll_work, DRM_OUTPUT_POLL_PERIOD);
-}
-EXPORT_SYMBOL(drm_kms_helper_poll_enable);
-
-/**
- * drm_kms_helper_poll_init - initialize and enable output polling
- * @dev: drm_device
- *
- * This function intializes and then also enables output polling support for
- * @dev. Drivers which do not have reliable hotplug support in hardware can use
- * this helper infrastructure to regularly poll such connectors for changes in
- * their connection state.
- *
- * Drivers can control which connectors are polled by setting the
- * DRM_CONNECTOR_POLL_CONNECT and DRM_CONNECTOR_POLL_DISCONNECT flags. On
- * connectors where probing live outputs can result in visual distortion drivers
- * should not set the DRM_CONNECTOR_POLL_DISCONNECT flag to avoid this.
- * Connectors which have no flag or only DRM_CONNECTOR_POLL_HPD set are
- * completely ignored by the polling logic.
- *
- * Note that a connector can be both polled and probed from the hotplug handler,
- * in case the hotplug interrupt is known to be unreliable.
- */
-void drm_kms_helper_poll_init(struct drm_device *dev)
-{
-	INIT_DELAYED_WORK(&dev->mode_config.output_poll_work, output_poll_execute);
-	dev->mode_config.poll_enabled = true;
-
-	drm_kms_helper_poll_enable(dev);
-}
-EXPORT_SYMBOL(drm_kms_helper_poll_init);
-
-/**
- * drm_kms_helper_poll_fini - disable output polling and clean it up
- * @dev: drm_device
- */
-void drm_kms_helper_poll_fini(struct drm_device *dev)
-{
-	drm_kms_helper_poll_disable(dev);
-}
-EXPORT_SYMBOL(drm_kms_helper_poll_fini);
-
-/**
- * drm_helper_hpd_irq_event - hotplug processing
- * @dev: drm_device
- *
- * Drivers can use this helper function to run a detect cycle on all connectors
- * which have the DRM_CONNECTOR_POLL_HPD flag set in their &polled member. All
- * other connectors are ignored, which is useful to avoid reprobing fixed
- * panels.
- *
- * This helper function is useful for drivers which can't or don't track hotplug
- * interrupts for each connector.
- *
- * Drivers which support hotplug interrupts for each connector individually and
- * which have a more fine-grained detect logic should bypass this code and
- * directly call drm_kms_helper_hotplug_event() in case the connector state
- * changed.
- *
- * This function must be called from process context with no mode
- * setting locks held.
- *
- * Note that a connector can be both polled and probed from the hotplug handler,
- * in case the hotplug interrupt is known to be unreliable.
- */
-bool drm_helper_hpd_irq_event(struct drm_device *dev)
-{
-	struct drm_connector *connector;
-	enum drm_connector_status old_status;
-	bool changed = false;
-
-	if (!dev->mode_config.poll_enabled)
-		return false;
-
-	mutex_lock(&dev->mode_config.mutex);
-	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
-
-		/* Only handle HPD capable connectors. */
-		if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
-			continue;
-
-		old_status = connector->status;
-
-		connector->status = connector->funcs->detect(connector, false);
-		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
-			      connector->base.id,
-			      drm_get_connector_name(connector),
-			      drm_get_connector_status_name(old_status),
-			      drm_get_connector_status_name(connector->status));
-		if (old_status != connector->status)
-			changed = true;
-	}
-
-	mutex_unlock(&dev->mode_config.mutex);
-
-	if (changed)
-		drm_kms_helper_hotplug_event(dev);
-
-	return changed;
-}
-EXPORT_SYMBOL(drm_helper_hpd_irq_event);
diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
new file mode 100644
index 000000000000..e70f54d4a581
--- /dev/null
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -0,0 +1,426 @@
+/*
+ * Copyright (c) 2006-2008 Intel Corporation
+ * Copyright (c) 2007 Dave Airlie <airlied@linux.ie>
+ *
+ * DRM core CRTC related functions
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting documentation, and
+ * that the name of the copyright holders not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  The copyright holders make no representations
+ * about the suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+ * OF THIS SOFTWARE.
+ *
+ * Authors:
+ *      Keith Packard
+ *	Eric Anholt <eric@anholt.net>
+ *      Dave Airlie <airlied@linux.ie>
+ *      Jesse Barnes <jesse.barnes@intel.com>
+ */
+
+#include <linux/export.h>
+#include <linux/moduleparam.h>
+
+#include <drm/drmP.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_crtc_helper.h>
+#include <drm/drm_fb_helper.h>
+#include <drm/drm_edid.h>
+
+/**
+ * DOC: output probing helper overview
+ *
+ * This library provides some helper code for output probing. It provides an
+ * implementation of the core connector->fill_modes interface with
+ * drm_helper_probe_single_connector_modes.
+ *
+ * It also provides support for polling connectors with a work item and for
+ * generic hotplug interrupt handling where the driver doesn't or cannot keep
+ * track of a per-connector hpd interrupt.
+ *
+ * This helper library can be used independently of the modeset helper library.
+ * Drivers can also overwrite different parts e.g. use their own hotplug
+ * handling code to avoid probing unrelated outputs.
+ */
+
+static bool drm_kms_helper_poll = true;
+module_param_named(poll, drm_kms_helper_poll, bool, 0600);
+
+static void drm_mode_validate_flag(struct drm_connector *connector,
+				   int flags)
+{
+	struct drm_display_mode *mode;
+
+	if (flags == (DRM_MODE_FLAG_DBLSCAN | DRM_MODE_FLAG_INTERLACE |
+		      DRM_MODE_FLAG_3D_MASK))
+		return;
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if ((mode->flags & DRM_MODE_FLAG_INTERLACE) &&
+				!(flags & DRM_MODE_FLAG_INTERLACE))
+			mode->status = MODE_NO_INTERLACE;
+		if ((mode->flags & DRM_MODE_FLAG_DBLSCAN) &&
+				!(flags & DRM_MODE_FLAG_DBLSCAN))
+			mode->status = MODE_NO_DBLESCAN;
+		if ((mode->flags & DRM_MODE_FLAG_3D_MASK) &&
+				!(flags & DRM_MODE_FLAG_3D_MASK))
+			mode->status = MODE_NO_STEREO;
+	}
+
+	return;
+}
+
+/**
+ * drm_helper_probe_single_connector_modes - get complete set of display modes
+ * @connector: connector to probe
+ * @maxX: max width for modes
+ * @maxY: max height for modes
+ *
+ * Based on the helper callbacks implemented by @connector try to detect all
+ * valid modes.  Modes will first be added to the connector's probed_modes list,
+ * then culled (based on validity and the @maxX, @maxY parameters) and put into
+ * the normal modes list.
+ *
+ * Intended to be use as a generic implementation of the ->fill_modes()
+ * @connector vfunc for drivers that use the crtc helpers for output mode
+ * filtering and detection.
+ *
+ * Returns:
+ * The number of modes found on @connector.
+ */
+int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
+					    uint32_t maxX, uint32_t maxY)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_display_mode *mode;
+	struct drm_connector_helper_funcs *connector_funcs =
+		connector->helper_private;
+	int count = 0;
+	int mode_flags = 0;
+	bool verbose_prune = true;
+
+	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
+
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
+			drm_get_connector_name(connector));
+	/* set all modes to the unverified state */
+	list_for_each_entry(mode, &connector->modes, head)
+		mode->status = MODE_UNVERIFIED;
+
+	if (connector->force) {
+		if (connector->force == DRM_FORCE_ON)
+			connector->status = connector_status_connected;
+		else
+			connector->status = connector_status_disconnected;
+		if (connector->funcs->force)
+			connector->funcs->force(connector);
+	} else {
+		connector->status = connector->funcs->detect(connector, true);
+	}
+
+	/* Re-enable polling in case the global poll config changed. */
+	if (drm_kms_helper_poll != dev->mode_config.poll_running)
+		drm_kms_helper_poll_enable(dev);
+
+	dev->mode_config.poll_running = drm_kms_helper_poll;
+
+	if (connector->status == connector_status_disconnected) {
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
+			connector->base.id, drm_get_connector_name(connector));
+		drm_mode_connector_update_edid_property(connector, NULL);
+		verbose_prune = false;
+		goto prune;
+	}
+
+#ifdef CONFIG_DRM_LOAD_EDID_FIRMWARE
+	count = drm_load_edid_firmware(connector);
+	if (count == 0)
+#endif
+		count = (*connector_funcs->get_modes)(connector);
+
+	if (count == 0 && connector->status == connector_status_connected)
+		count = drm_add_modes_noedid(connector, 1024, 768);
+	if (count == 0)
+		goto prune;
+
+	drm_mode_connector_list_update(connector);
+
+	if (maxX && maxY)
+		drm_mode_validate_size(dev, &connector->modes, maxX, maxY);
+
+	if (connector->interlace_allowed)
+		mode_flags |= DRM_MODE_FLAG_INTERLACE;
+	if (connector->doublescan_allowed)
+		mode_flags |= DRM_MODE_FLAG_DBLSCAN;
+	if (connector->stereo_allowed)
+		mode_flags |= DRM_MODE_FLAG_3D_MASK;
+	drm_mode_validate_flag(connector, mode_flags);
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if (mode->status == MODE_OK)
+			mode->status = connector_funcs->mode_valid(connector,
+								   mode);
+	}
+
+prune:
+	drm_mode_prune_invalid(dev, &connector->modes, verbose_prune);
+
+	if (list_empty(&connector->modes))
+		return 0;
+
+	list_for_each_entry(mode, &connector->modes, head)
+		mode->vrefresh = drm_mode_vrefresh(mode);
+
+	drm_mode_sort(&connector->modes);
+
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] probed modes :\n", connector->base.id,
+			drm_get_connector_name(connector));
+	list_for_each_entry(mode, &connector->modes, head) {
+		drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
+		drm_mode_debug_printmodeline(mode);
+	}
+
+	return count;
+}
+EXPORT_SYMBOL(drm_helper_probe_single_connector_modes);
+
+/**
+ * drm_kms_helper_hotplug_event - fire off KMS hotplug events
+ * @dev: drm_device whose connector state changed
+ *
+ * This function fires off the uevent for userspace and also calls the
+ * output_poll_changed function, which is most commonly used to inform the fbdev
+ * emulation code and allow it to update the fbcon output configuration.
+ *
+ * Drivers should call this from their hotplug handling code when a change is
+ * detected. Note that this function does not do any output detection of its
+ * own, like drm_helper_hpd_irq_event() does - this is assumed to be done by the
+ * driver already.
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ */
+void drm_kms_helper_hotplug_event(struct drm_device *dev)
+{
+	/* send a uevent + call fbdev */
+	drm_sysfs_hotplug_event(dev);
+	if (dev->mode_config.funcs->output_poll_changed)
+		dev->mode_config.funcs->output_poll_changed(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_hotplug_event);
+
+#define DRM_OUTPUT_POLL_PERIOD (10*HZ)
+static void output_poll_execute(struct work_struct *work)
+{
+	struct delayed_work *delayed_work = to_delayed_work(work);
+	struct drm_device *dev = container_of(delayed_work, struct drm_device, mode_config.output_poll_work);
+	struct drm_connector *connector;
+	enum drm_connector_status old_status;
+	bool repoll = false, changed = false;
+
+	if (!drm_kms_helper_poll)
+		return;
+
+	mutex_lock(&dev->mode_config.mutex);
+	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
+
+		/* Ignore forced connectors. */
+		if (connector->force)
+			continue;
+
+		/* Ignore HPD capable connectors and connectors where we don't
+		 * want any hotplug detection at all for polling. */
+		if (!connector->polled || connector->polled == DRM_CONNECTOR_POLL_HPD)
+			continue;
+
+		repoll = true;
+
+		old_status = connector->status;
+		/* if we are connected and don't want to poll for disconnect
+		   skip it */
+		if (old_status == connector_status_connected &&
+		    !(connector->polled & DRM_CONNECTOR_POLL_DISCONNECT))
+			continue;
+
+		connector->status = connector->funcs->detect(connector, false);
+		if (old_status != connector->status) {
+			const char *old, *new;
+
+			old = drm_get_connector_status_name(old_status);
+			new = drm_get_connector_status_name(connector->status);
+
+			DRM_DEBUG_KMS("[CONNECTOR:%d:%s] "
+				      "status updated from %s to %s\n",
+				      connector->base.id,
+				      drm_get_connector_name(connector),
+				      old, new);
+
+			changed = true;
+		}
+	}
+
+	mutex_unlock(&dev->mode_config.mutex);
+
+	if (changed)
+		drm_kms_helper_hotplug_event(dev);
+
+	if (repoll)
+		schedule_delayed_work(delayed_work, DRM_OUTPUT_POLL_PERIOD);
+}
+
+/**
+ * drm_kms_helper_poll_disable - disable output polling
+ * @dev: drm_device
+ *
+ * This function disables the output polling work.
+ *
+ * Drivers can call this helper from their device suspend implementation. It is
+ * not an error to call this even when output polling isn't enabled or arlready
+ * disabled.
+ */
+void drm_kms_helper_poll_disable(struct drm_device *dev)
+{
+	if (!dev->mode_config.poll_enabled)
+		return;
+	cancel_delayed_work_sync(&dev->mode_config.output_poll_work);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_disable);
+
+/**
+ * drm_kms_helper_poll_enable - re-enable output polling.
+ * @dev: drm_device
+ *
+ * This function re-enables the output polling work.
+ *
+ * Drivers can call this helper from their device resume implementation. It is
+ * an error to call this when the output polling support has not yet been set
+ * up.
+ */
+void drm_kms_helper_poll_enable(struct drm_device *dev)
+{
+	bool poll = false;
+	struct drm_connector *connector;
+
+	if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll)
+		return;
+
+	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
+		if (connector->polled & (DRM_CONNECTOR_POLL_CONNECT |
+					 DRM_CONNECTOR_POLL_DISCONNECT))
+			poll = true;
+	}
+
+	if (poll)
+		schedule_delayed_work(&dev->mode_config.output_poll_work, DRM_OUTPUT_POLL_PERIOD);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_enable);
+
+/**
+ * drm_kms_helper_poll_init - initialize and enable output polling
+ * @dev: drm_device
+ *
+ * This function intializes and then also enables output polling support for
+ * @dev. Drivers which do not have reliable hotplug support in hardware can use
+ * this helper infrastructure to regularly poll such connectors for changes in
+ * their connection state.
+ *
+ * Drivers can control which connectors are polled by setting the
+ * DRM_CONNECTOR_POLL_CONNECT and DRM_CONNECTOR_POLL_DISCONNECT flags. On
+ * connectors where probing live outputs can result in visual distortion drivers
+ * should not set the DRM_CONNECTOR_POLL_DISCONNECT flag to avoid this.
+ * Connectors which have no flag or only DRM_CONNECTOR_POLL_HPD set are
+ * completely ignored by the polling logic.
+ *
+ * Note that a connector can be both polled and probed from the hotplug handler,
+ * in case the hotplug interrupt is known to be unreliable.
+ */
+void drm_kms_helper_poll_init(struct drm_device *dev)
+{
+	INIT_DELAYED_WORK(&dev->mode_config.output_poll_work, output_poll_execute);
+	dev->mode_config.poll_enabled = true;
+
+	drm_kms_helper_poll_enable(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_init);
+
+/**
+ * drm_kms_helper_poll_fini - disable output polling and clean it up
+ * @dev: drm_device
+ */
+void drm_kms_helper_poll_fini(struct drm_device *dev)
+{
+	drm_kms_helper_poll_disable(dev);
+}
+EXPORT_SYMBOL(drm_kms_helper_poll_fini);
+
+/**
+ * drm_helper_hpd_irq_event - hotplug processing
+ * @dev: drm_device
+ *
+ * Drivers can use this helper function to run a detect cycle on all connectors
+ * which have the DRM_CONNECTOR_POLL_HPD flag set in their &polled member. All
+ * other connectors are ignored, which is useful to avoid reprobing fixed
+ * panels.
+ *
+ * This helper function is useful for drivers which can't or don't track hotplug
+ * interrupts for each connector.
+ *
+ * Drivers which support hotplug interrupts for each connector individually and
+ * which have a more fine-grained detect logic should bypass this code and
+ * directly call drm_kms_helper_hotplug_event() in case the connector state
+ * changed.
+ *
+ * This function must be called from process context with no mode
+ * setting locks held.
+ *
+ * Note that a connector can be both polled and probed from the hotplug handler,
+ * in case the hotplug interrupt is known to be unreliable.
+ */
+bool drm_helper_hpd_irq_event(struct drm_device *dev)
+{
+	struct drm_connector *connector;
+	enum drm_connector_status old_status;
+	bool changed = false;
+
+	if (!dev->mode_config.poll_enabled)
+		return false;
+
+	mutex_lock(&dev->mode_config.mutex);
+	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
+
+		/* Only handle HPD capable connectors. */
+		if (!(connector->polled & DRM_CONNECTOR_POLL_HPD))
+			continue;
+
+		old_status = connector->status;
+
+		connector->status = connector->funcs->detect(connector, false);
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
+			      connector->base.id,
+			      drm_get_connector_name(connector),
+			      drm_get_connector_status_name(old_status),
+			      drm_get_connector_status_name(connector->status));
+		if (old_status != connector->status)
+			changed = true;
+	}
+
+	mutex_unlock(&dev->mode_config.mutex);
+
+	if (changed)
+		drm_kms_helper_hotplug_event(dev);
+
+	return changed;
+}
+EXPORT_SYMBOL(drm_helper_hpd_irq_event);