thunderbolt: Add control channel interface

Thunderbolt devices are configured by reading/writing into their
configuration space (similar to pci). This is done by sending packets
through the NHI (native host interface) onto the control channel.

This patch handles the low level packet based protocol and exposes
higher level operations like tb_cfg_read/tb_cfg_write.

Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 731 insertions, 0 deletions

diff --git a/drivers/thunderbolt/ctl.c b/drivers/thunderbolt/ctl.c
new file mode 100644
index 000000000000..9b0120bede51
--- /dev/null
+++ b/drivers/thunderbolt/ctl.c
@@ -0,0 +1,731 @@
+/*
+ * Thunderbolt Cactus Ridge driver - control channel and configuration commands
+ *
+ * Copyright (c) 2014 Andreas Noever <andreas.noever@gmail.com>
+ */
+
+#include <linux/crc32.h>
+#include <linux/slab.h>
+#include <linux/pci.h>
+#include <linux/dmapool.h>
+#include <linux/workqueue.h>
+#include <linux/kfifo.h>
+
+#include "ctl.h"
+
+
+struct ctl_pkg {
+	struct tb_ctl *ctl;
+	void *buffer;
+	struct ring_frame frame;
+};
+
+#define TB_CTL_RX_PKG_COUNT 10
+
+/**
+ * struct tb_cfg - thunderbolt control channel
+ */
+struct tb_ctl {
+	struct tb_nhi *nhi;
+	struct tb_ring *tx;
+	struct tb_ring *rx;
+
+	struct dma_pool *frame_pool;
+	struct ctl_pkg *rx_packets[TB_CTL_RX_PKG_COUNT];
+	DECLARE_KFIFO(response_fifo, struct ctl_pkg*, 16);
+	struct completion response_ready;
+
+	hotplug_cb callback;
+	void *callback_data;
+};
+
+
+#define tb_ctl_WARN(ctl, format, arg...) \
+	dev_WARN(&(ctl)->nhi->pdev->dev, format, ## arg)
+
+#define tb_ctl_err(ctl, format, arg...) \
+	dev_err(&(ctl)->nhi->pdev->dev, format, ## arg)
+
+#define tb_ctl_warn(ctl, format, arg...) \
+	dev_warn(&(ctl)->nhi->pdev->dev, format, ## arg)
+
+#define tb_ctl_info(ctl, format, arg...) \
+	dev_info(&(ctl)->nhi->pdev->dev, format, ## arg)
+
+
+/* configuration packets definitions */
+
+enum tb_cfg_pkg_type {
+	TB_CFG_PKG_READ = 1,
+	TB_CFG_PKG_WRITE = 2,
+	TB_CFG_PKG_ERROR = 3,
+	TB_CFG_PKG_NOTIFY_ACK = 4,
+	TB_CFG_PKG_EVENT = 5,
+	TB_CFG_PKG_XDOMAIN_REQ = 6,
+	TB_CFG_PKG_XDOMAIN_RESP = 7,
+	TB_CFG_PKG_OVERRIDE = 8,
+	TB_CFG_PKG_RESET = 9,
+	TB_CFG_PKG_PREPARE_TO_SLEEP = 0xd,
+};
+
+/* common header */
+struct tb_cfg_header {
+	u32 route_hi:22;
+	u32 unknown:10; /* highest order bit is set on replies */
+	u32 route_lo;
+} __packed;
+
+/* additional header for read/write packets */
+struct tb_cfg_address {
+	u32 offset:13; /* in dwords */
+	u32 length:6; /* in dwords */
+	u32 port:6;
+	enum tb_cfg_space space:2;
+	u32 seq:2; /* sequence number  */
+	u32 zero:3;
+} __packed;
+
+/* TB_CFG_PKG_READ, response for TB_CFG_PKG_WRITE */
+struct cfg_read_pkg {
+	struct tb_cfg_header header;
+	struct tb_cfg_address addr;
+} __packed;
+
+/* TB_CFG_PKG_WRITE, response for TB_CFG_PKG_READ */
+struct cfg_write_pkg {
+	struct tb_cfg_header header;
+	struct tb_cfg_address addr;
+	u32 data[64]; /* maximum size, tb_cfg_address.length has 6 bits */
+} __packed;
+
+/* TB_CFG_PKG_ERROR */
+struct cfg_error_pkg {
+	struct tb_cfg_header header;
+	enum tb_cfg_error error:4;
+	u32 zero1:4;
+	u32 port:6;
+	u32 zero2:2; /* Both should be zero, still they are different fields. */
+	u32 zero3:16;
+} __packed;
+
+/* TB_CFG_PKG_EVENT */
+struct cfg_event_pkg {
+	struct tb_cfg_header header;
+	u32 port:6;
+	u32 zero:25;
+	bool unplug:1;
+} __packed;
+
+/* TB_CFG_PKG_RESET */
+struct cfg_reset_pkg {
+	struct tb_cfg_header header;
+} __packed;
+
+/* TB_CFG_PKG_PREPARE_TO_SLEEP */
+struct cfg_pts_pkg {
+	struct tb_cfg_header header;
+	u32 data;
+} __packed;
+
+
+/* utility functions */
+
+static u64 get_route(struct tb_cfg_header header)
+{
+	return (u64) header.route_hi << 32 | header.route_lo;
+}
+
+static struct tb_cfg_header make_header(u64 route)
+{
+	struct tb_cfg_header header = {
+		.route_hi = route >> 32,
+		.route_lo = route,
+	};
+	/* check for overflow, route_hi is not 32 bits! */
+	WARN_ON(get_route(header) != route);
+	return header;
+}
+
+static int check_header(struct ctl_pkg *pkg, u32 len, enum tb_cfg_pkg_type type,
+			u64 route)
+{
+	struct tb_cfg_header *header = pkg->buffer;
+
+	/* check frame, TODO: frame flags */
+	if (WARN(len != pkg->frame.size,
+			"wrong framesize (expected %#x, got %#x)\n",
+			len, pkg->frame.size))
+		return -EIO;
+	if (WARN(type != pkg->frame.eof, "wrong eof (expected %#x, got %#x)\n",
+			type, pkg->frame.eof))
+		return -EIO;
+	if (WARN(pkg->frame.sof, "wrong sof (expected 0x0, got %#x)\n",
+			pkg->frame.sof))
+		return -EIO;
+
+	/* check header */
+	if (WARN(header->unknown != 1 << 9,
+			"header->unknown is %#x\n", header->unknown))
+		return -EIO;
+	if (WARN(route != get_route(*header),
+			"wrong route (expected %llx, got %llx)",
+			route, get_route(*header)))
+		return -EIO;
+	return 0;
+}
+
+static int check_config_address(struct tb_cfg_address addr,
+				enum tb_cfg_space space, u32 offset,
+				u32 length)
+{
+	if (WARN(addr.zero, "addr.zero is %#x\n", addr.zero))
+		return -EIO;
+	if (WARN(space != addr.space, "wrong space (expected %x, got %x\n)",
+			space, addr.space))
+		return -EIO;
+	if (WARN(offset != addr.offset, "wrong offset (expected %x, got %x\n)",
+			offset, addr.offset))
+		return -EIO;
+	if (WARN(length != addr.length, "wrong space (expected %x, got %x\n)",
+			length, addr.length))
+		return -EIO;
+	if (WARN(addr.seq, "addr.seq is %#x\n", addr.seq))
+		return -EIO;
+	/*
+	 * We cannot check addr->port as it is set to the upstream port of the
+	 * sender.
+	 */
+	return 0;
+}
+
+static struct tb_cfg_result decode_error(struct ctl_pkg *response)
+{
+	struct cfg_error_pkg *pkg = response->buffer;
+	struct tb_cfg_result res = { 0 };
+	res.response_route = get_route(pkg->header);
+	res.response_port = 0;
+	res.err = check_header(response, sizeof(*pkg), TB_CFG_PKG_ERROR,
+			       get_route(pkg->header));
+	if (res.err)
+		return res;
+
+	WARN(pkg->zero1, "pkg->zero1 is %#x\n", pkg->zero1);
+	WARN(pkg->zero2, "pkg->zero1 is %#x\n", pkg->zero1);
+	WARN(pkg->zero3, "pkg->zero1 is %#x\n", pkg->zero1);
+	res.err = 1;
+	res.tb_error = pkg->error;
+	res.response_port = pkg->port;
+	return res;
+
+}
+
+static struct tb_cfg_result parse_header(struct ctl_pkg *pkg, u32 len,
+					 enum tb_cfg_pkg_type type, u64 route)
+{
+	struct tb_cfg_header *header = pkg->buffer;
+	struct tb_cfg_result res = { 0 };
+
+	if (pkg->frame.eof == TB_CFG_PKG_ERROR)
+		return decode_error(pkg);
+
+	res.response_port = 0; /* will be updated later for cfg_read/write */
+	res.response_route = get_route(*header);
+	res.err = check_header(pkg, len, type, route);
+	return res;
+}
+
+static void tb_cfg_print_error(struct tb_ctl *ctl,
+			       const struct tb_cfg_result *res)
+{
+	WARN_ON(res->err != 1);
+	switch (res->tb_error) {
+	case TB_CFG_ERROR_PORT_NOT_CONNECTED:
+		/* Port is not connected. This can happen during surprise
+		 * removal. Do not warn. */
+		return;
+	case TB_CFG_ERROR_INVALID_CONFIG_SPACE:
+		/*
+		 * Invalid cfg_space/offset/length combination in
+		 * cfg_read/cfg_write.
+		 */
+		tb_ctl_WARN(ctl,
+			"CFG_ERROR(%llx:%x): Invalid config space of offset\n",
+			res->response_route, res->response_port);
+		return;
+	case TB_CFG_ERROR_NO_SUCH_PORT:
+		/*
+		 * - The route contains a non-existent port.
+		 * - The route contains a non-PHY port (e.g. PCIe).
+		 * - The port in cfg_read/cfg_write does not exist.
+		 */
+		tb_ctl_WARN(ctl, "CFG_ERROR(%llx:%x): Invalid port\n",
+			res->response_route, res->response_port);
+		return;
+	case TB_CFG_ERROR_LOOP:
+		tb_ctl_WARN(ctl, "CFG_ERROR(%llx:%x): Route contains a loop\n",
+			res->response_route, res->response_port);
+		return;
+	default:
+		/* 5,6,7,9 and 11 are also valid error codes */
+		tb_ctl_WARN(ctl, "CFG_ERROR(%llx:%x): Unknown error\n",
+			res->response_route, res->response_port);
+		return;
+	}
+}
+
+static void cpu_to_be32_array(__be32 *dst, u32 *src, size_t len)
+{
+	int i;
+	for (i = 0; i < len; i++)
+		dst[i] = cpu_to_be32(src[i]);
+}
+
+static void be32_to_cpu_array(u32 *dst, __be32 *src, size_t len)
+{
+	int i;
+	for (i = 0; i < len; i++)
+		dst[i] = be32_to_cpu(src[i]);
+}
+
+static __be32 tb_crc(void *data, size_t len)
+{
+	return cpu_to_be32(~__crc32c_le(~0, data, len));
+}
+
+static void tb_ctl_pkg_free(struct ctl_pkg *pkg)
+{
+	if (pkg) {
+		dma_pool_free(pkg->ctl->frame_pool,
+			      pkg->buffer, pkg->frame.buffer_phy);
+		kfree(pkg);
+	}
+}
+
+static struct ctl_pkg *tb_ctl_pkg_alloc(struct tb_ctl *ctl)
+{
+	struct ctl_pkg *pkg = kzalloc(sizeof(*pkg), GFP_KERNEL);
+	if (!pkg)
+		return 0;
+	pkg->ctl = ctl;
+	pkg->buffer = dma_pool_alloc(ctl->frame_pool, GFP_KERNEL,
+				     &pkg->frame.buffer_phy);
+	if (!pkg->buffer) {
+		kfree(pkg);
+		return 0;
+	}
+	return pkg;
+}
+
+
+/* RX/TX handling */
+
+static void tb_ctl_tx_callback(struct tb_ring *ring, struct ring_frame *frame,
+			       bool canceled)
+{
+	struct ctl_pkg *pkg = container_of(frame, typeof(*pkg), frame);
+	tb_ctl_pkg_free(pkg);
+}
+
+/**
+ * tb_cfg_tx() - transmit a packet on the control channel
+ *
+ * len must be a multiple of four.
+ *
+ * Return: Returns 0 on success or an error code on failure.
+ */
+static int tb_ctl_tx(struct tb_ctl *ctl, void *data, size_t len,
+		     enum tb_cfg_pkg_type type)
+{
+	int res;
+	struct ctl_pkg *pkg;
+	if (len % 4 != 0) { /* required for le->be conversion */
+		tb_ctl_WARN(ctl, "TX: invalid size: %zu\n", len);
+		return -EINVAL;
+	}
+	if (len > TB_FRAME_SIZE - 4) { /* checksum is 4 bytes */
+		tb_ctl_WARN(ctl, "TX: packet too large: %zu/%d\n",
+			    len, TB_FRAME_SIZE - 4);
+		return -EINVAL;
+	}
+	pkg = tb_ctl_pkg_alloc(ctl);
+	if (!pkg)
+		return -ENOMEM;
+	pkg->frame.callback = tb_ctl_tx_callback;
+	pkg->frame.size = len + 4;
+	pkg->frame.sof = type;
+	pkg->frame.eof = type;
+	cpu_to_be32_array(pkg->buffer, data, len / 4);
+	*(u32 *) (pkg->buffer + len) = tb_crc(pkg->buffer, len);
+
+	res = ring_tx(ctl->tx, &pkg->frame);
+	if (res) /* ring is stopped */
+		tb_ctl_pkg_free(pkg);
+	return res;
+}
+
+/**
+ * tb_ctl_handle_plug_event() - acknowledge a plug event, invoke ctl->callback
+ */
+static void tb_ctl_handle_plug_event(struct tb_ctl *ctl,
+				     struct ctl_pkg *response)
+{
+	struct cfg_event_pkg *pkg = response->buffer;
+	u64 route = get_route(pkg->header);
+
+	if (check_header(response, sizeof(*pkg), TB_CFG_PKG_EVENT, route)) {
+		tb_ctl_warn(ctl, "malformed TB_CFG_PKG_EVENT\n");
+		return;
+	}
+
+	if (tb_cfg_error(ctl, route, pkg->port, TB_CFG_ERROR_ACK_PLUG_EVENT))
+		tb_ctl_warn(ctl, "could not ack plug event on %llx:%x\n",
+			    route, pkg->port);
+	WARN(pkg->zero, "pkg->zero is %#x\n", pkg->zero);
+	ctl->callback(ctl->callback_data, route, pkg->port, pkg->unplug);
+}
+
+static void tb_ctl_rx_submit(struct ctl_pkg *pkg)
+{
+	ring_rx(pkg->ctl->rx, &pkg->frame); /*
+					     * We ignore failures during stop.
+					     * All rx packets are referenced
+					     * from ctl->rx_packets, so we do
+					     * not loose them.
+					     */
+}
+
+static void tb_ctl_rx_callback(struct tb_ring *ring, struct ring_frame *frame,
+			       bool canceled)
+{
+	struct ctl_pkg *pkg = container_of(frame, typeof(*pkg), frame);
+
+	if (canceled)
+		return; /*
+			 * ring is stopped, packet is referenced from
+			 * ctl->rx_packets.
+			 */
+
+	if (frame->size < 4 || frame->size % 4 != 0) {
+		tb_ctl_err(pkg->ctl, "RX: invalid size %#x, dropping packet\n",
+			   frame->size);
+		goto rx;
+	}
+
+	frame->size -= 4; /* remove checksum */
+	if (*(u32 *) (pkg->buffer + frame->size)
+			!= tb_crc(pkg->buffer, frame->size)) {
+		tb_ctl_err(pkg->ctl,
+			   "RX: checksum mismatch, dropping packet\n");
+		goto rx;
+	}
+	be32_to_cpu_array(pkg->buffer, pkg->buffer, frame->size / 4);
+
+	if (frame->eof == TB_CFG_PKG_EVENT) {
+		tb_ctl_handle_plug_event(pkg->ctl, pkg);
+		goto rx;
+	}
+	if (!kfifo_put(&pkg->ctl->response_fifo, pkg)) {
+		tb_ctl_err(pkg->ctl, "RX: fifo is full\n");
+		goto rx;
+	}
+	complete(&pkg->ctl->response_ready);
+	return;
+rx:
+	tb_ctl_rx_submit(pkg);
+}
+
+/**
+ * tb_ctl_rx() - receive a packet from the control channel
+ */
+static struct tb_cfg_result tb_ctl_rx(struct tb_ctl *ctl, void *buffer,
+				      size_t length, int timeout_msec,
+				      u8 route, enum tb_cfg_pkg_type type)
+{
+	struct tb_cfg_result res;
+	struct ctl_pkg *pkg;
+
+	if (!wait_for_completion_timeout(&ctl->response_ready,
+					 msecs_to_jiffies(timeout_msec))) {
+		tb_ctl_WARN(ctl, "RX: timeout\n");
+		return (struct tb_cfg_result) { .err = -ETIMEDOUT };
+	}
+	if (!kfifo_get(&ctl->response_fifo, &pkg)) {
+		tb_ctl_WARN(ctl, "empty kfifo\n");
+		return (struct tb_cfg_result) { .err = -EIO };
+	}
+
+	res = parse_header(pkg, length, type, route);
+	if (!res.err)
+		memcpy(buffer, pkg->buffer, length);
+	tb_ctl_rx_submit(pkg);
+	return res;
+}
+
+
+/* public interface, alloc/start/stop/free */
+
+/**
+ * tb_ctl_alloc() - allocate a control channel
+ *
+ * cb will be invoked once for every hot plug event.
+ *
+ * Return: Returns a pointer on success or NULL on failure.
+ */
+struct tb_ctl *tb_ctl_alloc(struct tb_nhi *nhi, hotplug_cb cb, void *cb_data)
+{
+	int i;
+	struct tb_ctl *ctl = kzalloc(sizeof(*ctl), GFP_KERNEL);
+	if (!ctl)
+		return NULL;
+	ctl->nhi = nhi;
+	ctl->callback = cb;
+	ctl->callback_data = cb_data;
+
+	init_completion(&ctl->response_ready);
+	INIT_KFIFO(ctl->response_fifo);
+	ctl->frame_pool = dma_pool_create("thunderbolt_ctl", &nhi->pdev->dev,
+					 TB_FRAME_SIZE, 4, 0);
+	if (!ctl->frame_pool)
+		goto err;
+
+	ctl->tx = ring_alloc_tx(nhi, 0, 10);
+	if (!ctl->tx)
+		goto err;
+
+	ctl->rx = ring_alloc_rx(nhi, 0, 10);
+	if (!ctl->rx)
+		goto err;
+
+	for (i = 0; i < TB_CTL_RX_PKG_COUNT; i++) {
+		ctl->rx_packets[i] = tb_ctl_pkg_alloc(ctl);
+		if (!ctl->rx_packets[i])
+			goto err;
+		ctl->rx_packets[i]->frame.callback = tb_ctl_rx_callback;
+	}
+
+	tb_ctl_info(ctl, "control channel created\n");
+	return ctl;
+err:
+	tb_ctl_free(ctl);
+	return NULL;
+}
+
+/**
+ * tb_ctl_free() - free a control channel
+ *
+ * Must be called after tb_ctl_stop.
+ *
+ * Must NOT be called from ctl->callback.
+ */
+void tb_ctl_free(struct tb_ctl *ctl)
+{
+	int i;
+	if (ctl->rx)
+		ring_free(ctl->rx);
+	if (ctl->tx)
+		ring_free(ctl->tx);
+
+	/* free RX packets */
+	for (i = 0; i < TB_CTL_RX_PKG_COUNT; i++)
+		tb_ctl_pkg_free(ctl->rx_packets[i]);
+
+
+	if (ctl->frame_pool)
+		dma_pool_destroy(ctl->frame_pool);
+	kfree(ctl);
+}
+
+/**
+ * tb_cfg_start() - start/resume the control channel
+ */
+void tb_ctl_start(struct tb_ctl *ctl)
+{
+	int i;
+	tb_ctl_info(ctl, "control channel starting...\n");
+	ring_start(ctl->tx); /* is used to ack hotplug packets, start first */
+	ring_start(ctl->rx);
+	for (i = 0; i < TB_CTL_RX_PKG_COUNT; i++)
+		tb_ctl_rx_submit(ctl->rx_packets[i]);
+}
+
+/**
+ * control() - pause the control channel
+ *
+ * All invocations of ctl->callback will have finished after this method
+ * returns.
+ *
+ * Must NOT be called from ctl->callback.
+ */
+void tb_ctl_stop(struct tb_ctl *ctl)
+{
+	ring_stop(ctl->rx);
+	ring_stop(ctl->tx);
+
+	if (!kfifo_is_empty(&ctl->response_fifo))
+		tb_ctl_WARN(ctl, "dangling response in response_fifo\n");
+	kfifo_reset(&ctl->response_fifo);
+	tb_ctl_info(ctl, "control channel stopped\n");
+}
+
+/* public interface, commands */
+
+/**
+ * tb_cfg_error() - send error packet
+ *
+ * Return: Returns 0 on success or an error code on failure.
+ */
+int tb_cfg_error(struct tb_ctl *ctl, u64 route, u32 port,
+		 enum tb_cfg_error error)
+{
+	struct cfg_error_pkg pkg = {
+		.header = make_header(route),
+		.port = port,
+		.error = error,
+	};
+	tb_ctl_info(ctl, "resetting error on %llx:%x.\n", route, port);
+	return tb_ctl_tx(ctl, &pkg, sizeof(pkg), TB_CFG_PKG_ERROR);
+}
+
+/**
+ * tb_cfg_reset() - send a reset packet and wait for a response
+ *
+ * If the switch at route is incorrectly configured then we will not receive a
+ * reply (even though the switch will reset). The caller should check for
+ * -ETIMEDOUT and attempt to reconfigure the switch.
+ */
+struct tb_cfg_result tb_cfg_reset(struct tb_ctl *ctl, u64 route,
+				  int timeout_msec)
+{
+	int err;
+	struct cfg_reset_pkg request = { .header = make_header(route) };
+	struct tb_cfg_header reply;
+
+	err = tb_ctl_tx(ctl, &request, sizeof(request), TB_CFG_PKG_RESET);
+	if (err)
+		return (struct tb_cfg_result) { .err = err };
+
+	return tb_ctl_rx(ctl, &reply, sizeof(reply), timeout_msec, route,
+			 TB_CFG_PKG_RESET);
+}
+
+/**
+ * tb_cfg_read() - read from config space into buffer
+ *
+ * Offset and length are in dwords.
+ */
+struct tb_cfg_result tb_cfg_read_raw(struct tb_ctl *ctl, void *buffer,
+		u64 route, u32 port, enum tb_cfg_space space,
+		u32 offset, u32 length, int timeout_msec)
+{
+	struct tb_cfg_result res = { 0 };
+	struct cfg_read_pkg request = {
+		.header = make_header(route),
+		.addr = {
+			.port = port,
+			.space = space,
+			.offset = offset,
+			.length = length,
+		},
+	};
+	struct cfg_write_pkg reply;
+
+	res.err = tb_ctl_tx(ctl, &request, sizeof(request), TB_CFG_PKG_READ);
+	if (res.err)
+		return res;
+
+	res = tb_ctl_rx(ctl, &reply, 12 + 4 * length, timeout_msec, route,
+			TB_CFG_PKG_READ);
+	if (res.err)
+		return res;
+
+	res.response_port = reply.addr.port;
+	res.err = check_config_address(reply.addr, space, offset, length);
+	if (!res.err)
+		memcpy(buffer, &reply.data, 4 * length);
+	return res;
+}
+
+/**
+ * tb_cfg_write() - write from buffer into config space
+ *
+ * Offset and length are in dwords.
+ */
+struct tb_cfg_result tb_cfg_write_raw(struct tb_ctl *ctl, void *buffer,
+		u64 route, u32 port, enum tb_cfg_space space,
+		u32 offset, u32 length, int timeout_msec)
+{
+	struct tb_cfg_result res = { 0 };
+	struct cfg_write_pkg request = {
+		.header = make_header(route),
+		.addr = {
+			.port = port,
+			.space = space,
+			.offset = offset,
+			.length = length,
+		},
+	};
+	struct cfg_read_pkg reply;
+
+	memcpy(&request.data, buffer, length * 4);
+
+	res.err = tb_ctl_tx(ctl, &request, 12 + 4 * length, TB_CFG_PKG_WRITE);
+	if (res.err)
+		return res;
+
+	res = tb_ctl_rx(ctl, &reply, sizeof(reply), timeout_msec, route,
+			TB_CFG_PKG_WRITE);
+	if (res.err)
+		return res;
+
+	res.response_port = reply.addr.port;
+	res.err = check_config_address(reply.addr, space, offset, length);
+	return res;
+}
+
+int tb_cfg_read(struct tb_ctl *ctl, void *buffer, u64 route, u32 port,
+		enum tb_cfg_space space, u32 offset, u32 length)
+{
+	struct tb_cfg_result res = tb_cfg_read_raw(ctl, buffer, route, port,
+			space, offset, length, TB_CFG_DEFAULT_TIMEOUT);
+	if (res.err == 1) {
+		tb_cfg_print_error(ctl, &res);
+		return -EIO;
+	}
+	WARN(res.err, "tb_cfg_read: %d\n", res.err);
+	return res.err;
+}
+
+int tb_cfg_write(struct tb_ctl *ctl, void *buffer, u64 route, u32 port,
+		 enum tb_cfg_space space, u32 offset, u32 length)
+{
+	struct tb_cfg_result res = tb_cfg_write_raw(ctl, buffer, route, port,
+			space, offset, length, TB_CFG_DEFAULT_TIMEOUT);
+	if (res.err == 1) {
+		tb_cfg_print_error(ctl, &res);
+		return -EIO;
+	}
+	WARN(res.err, "tb_cfg_write: %d\n", res.err);
+	return res.err;
+}
+
+/**
+ * tb_cfg_get_upstream_port() - get upstream port number of switch at route
+ *
+ * Reads the first dword from the switches TB_CFG_SWITCH config area and
+ * returns the port number from which the reply originated.
+ *
+ * Return: Returns the upstream port number on success or an error code on
+ * failure.
+ */
+int tb_cfg_get_upstream_port(struct tb_ctl *ctl, u64 route)
+{
+	u32 dummy;
+	struct tb_cfg_result res = tb_cfg_read_raw(ctl, &dummy, route, 0,
+						   TB_CFG_SWITCH, 0, 1,
+						   TB_CFG_DEFAULT_TIMEOUT);
+	if (res.err == 1)
+		return -EIO;
+	if (res.err)
+		return res.err;
+	return res.response_port;
+}