[PATCH v4 18/27] thunderbolt: Rework control channel to be more reliable

[Mika Westerberg]

If a request times out the response might arrive right after the request
is failed. This response is pushed to the kfifo and next request will
read it instead. Since it most likely will not pass our validation
checks in parse_header() the next request will fail as well, and
response to that request will be pushed to the kfifo, ad infinitum.

We end up in a situation where all requests fail and no devices can be
added anymore until the driver is unloaded and reloaded again.

To overcome this, rework the control channel so that we will have a
queue of outstanding requests. Each request will be handled in turn and
the response is validated against what is expected. Unexpected packets
(for example responses for requests that have been timed out) are
dropped. This model is copied from Greybus implementation with small
changes here and there to get it cope with Thunderbolt control packets.

In addition the configuration packets support sequence number which the
switch is supposed to copy from the request to response. We use this to
drop responses that are already timed out. Taking advantage of the
sequence number, we automatically retry configuration read/write 4 times
before giving up.

Also timeout is not a programming error so there is no need to trigger a
scary backtrace (WARN), instead we just log a warning.  After all
Thunderbolt devices are hot-pluggable by definition which means user can
unplug a device any time and that is totally acceptable.

With this change there is no need to take the global domain lock when
sending configuration packets anymore. This is useful when we add
support for cross-domain (XDomain) communication later on.

Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Reviewed-by: Yehezkel Bernat <yehezkel.bernat@xxxxxxxxx>
Reviewed-by: Michael Jamet <michael.jamet@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Andreas Noever <andreas.noever@xxxxxxxxx>
---
 drivers/thunderbolt/ctl.c | 477 +++++++++++++++++++++++++++++++++++++++-------
 drivers/thunderbolt/ctl.h |  65 +++++++
 drivers/thunderbolt/tb.h  |   2 +-
 3 files changed, 473 insertions(+), 71 deletions(-)

diff --git a/drivers/thunderbolt/ctl.c b/drivers/thunderbolt/ctl.c
index 5417ed244edc..27c30ff79a84 100644
--- a/drivers/thunderbolt/ctl.c
+++ b/drivers/thunderbolt/ctl.c
@@ -5,22 +5,17 @@
  */
 
 #include <linux/crc32.h>
+#include <linux/delay.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
+#define TB_CTL_RX_PKG_COUNT	10
+#define TB_CTL_RETRIES		4
 
 /**
  * struct tb_cfg - thunderbolt control channel
@@ -32,8 +27,9 @@ struct tb_ctl {
 
 	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;
+	struct mutex request_queue_lock;
+	struct list_head request_queue;
+	bool running;
 
 	event_cb callback;
 	void *callback_data;
@@ -55,10 +51,121 @@ struct tb_ctl {
 #define tb_ctl_dbg(ctl, format, arg...) \
 	dev_dbg(&(ctl)->nhi->pdev->dev, format, ## arg)
 
+static DECLARE_WAIT_QUEUE_HEAD(tb_cfg_request_cancel_queue);
+/* Serializes access to request kref_get/put */
+static DEFINE_MUTEX(tb_cfg_request_lock);
+
+/**
+ * tb_cfg_request_alloc() - Allocates a new config request
+ *
+ * This is refcounted object so when you are done with this, call
+ * tb_cfg_request_put() to it.
+ */
+struct tb_cfg_request *tb_cfg_request_alloc(void)
+{
+	struct tb_cfg_request *req;
+
+	req = kzalloc(sizeof(*req), GFP_KERNEL);
+	if (!req)
+		return NULL;
+
+	kref_init(&req->kref);
+
+	return req;
+}
+
+/**
+ * tb_cfg_request_get() - Increase refcount of a request
+ * @req: Request whose refcount is increased
+ */
+void tb_cfg_request_get(struct tb_cfg_request *req)
+{
+	mutex_lock(&tb_cfg_request_lock);
+	kref_get(&req->kref);
+	mutex_unlock(&tb_cfg_request_lock);
+}
+
+static void tb_cfg_request_destroy(struct kref *kref)
+{
+	struct tb_cfg_request *req = container_of(kref, typeof(*req), kref);
+
+	kfree(req);
+}
+
+/**
+ * tb_cfg_request_put() - Decrease refcount and possibly release the request
+ * @req: Request whose refcount is decreased
+ *
+ * Call this function when you are done with the request. When refcount
+ * goes to %0 the object is released.
+ */
+void tb_cfg_request_put(struct tb_cfg_request *req)
+{
+	mutex_lock(&tb_cfg_request_lock);
+	kref_put(&req->kref, tb_cfg_request_destroy);
+	mutex_unlock(&tb_cfg_request_lock);
+}
+
+static int tb_cfg_request_enqueue(struct tb_ctl *ctl,
+				  struct tb_cfg_request *req)
+{
+	WARN_ON(test_bit(TB_CFG_REQUEST_ACTIVE, &req->flags));
+	WARN_ON(req->ctl);
+
+	mutex_lock(&ctl->request_queue_lock);
+	if (!ctl->running) {
+		mutex_unlock(&ctl->request_queue_lock);
+		return -ENOTCONN;
+	}
+	req->ctl = ctl;
+	list_add_tail(&req->list, &ctl->request_queue);
+	set_bit(TB_CFG_REQUEST_ACTIVE, &req->flags);
+	mutex_unlock(&ctl->request_queue_lock);
+	return 0;
+}
+
+static void tb_cfg_request_dequeue(struct tb_cfg_request *req)
+{
+	struct tb_ctl *ctl = req->ctl;
+
+	mutex_lock(&ctl->request_queue_lock);
+	list_del(&req->list);
+	clear_bit(TB_CFG_REQUEST_ACTIVE, &req->flags);
+	if (test_bit(TB_CFG_REQUEST_CANCELED, &req->flags))
+		wake_up(&tb_cfg_request_cancel_queue);
+	mutex_unlock(&ctl->request_queue_lock);
+}
+
+static bool tb_cfg_request_is_active(struct tb_cfg_request *req)
+{
+	return test_bit(TB_CFG_REQUEST_ACTIVE, &req->flags);
+}
+
+static struct tb_cfg_request *
+tb_cfg_request_find(struct tb_ctl *ctl, struct ctl_pkg *pkg)
+{
+	struct tb_cfg_request *req;
+	bool found = false;
+
+	mutex_lock(&pkg->ctl->request_queue_lock);
+	list_for_each_entry(req, &pkg->ctl->request_queue, list) {
+		tb_cfg_request_get(req);
+		if (req->match(req, pkg)) {
+			found = true;
+			break;
+		}
+		tb_cfg_request_put(req);
+	}
+	mutex_unlock(&pkg->ctl->request_queue_lock);
+
+	return found ? req : NULL;
+}
+
 /* utility functions */
 
-static int check_header(struct ctl_pkg *pkg, u32 len, enum tb_cfg_pkg_type type,
-			u64 route)
+
+static int check_header(const struct ctl_pkg *pkg, u32 len,
+			enum tb_cfg_pkg_type type, u64 route)
 {
 	struct tb_cfg_header *header = pkg->buffer;
 
@@ -100,8 +207,6 @@ static int check_config_address(struct tb_cfg_address addr,
 	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.
@@ -109,7 +214,7 @@ static int check_config_address(struct tb_cfg_address addr,
 	return 0;
 }
 
-static struct tb_cfg_result decode_error(struct ctl_pkg *response)
+static struct tb_cfg_result decode_error(const struct ctl_pkg *response)
 {
 	struct cfg_error_pkg *pkg = response->buffer;
 	struct tb_cfg_result res = { 0 };
@@ -130,7 +235,7 @@ static struct tb_cfg_result decode_error(struct ctl_pkg *response)
 
 }
 
-static struct tb_cfg_result parse_header(struct ctl_pkg *pkg, u32 len,
+static struct tb_cfg_result parse_header(const struct ctl_pkg *pkg, u32 len,
 					 enum tb_cfg_pkg_type type, u64 route)
 {
 	struct tb_cfg_header *header = pkg->buffer;
@@ -198,7 +303,7 @@ static void be32_to_cpu_array(u32 *dst, __be32 *src, size_t len)
 		dst[i] = be32_to_cpu(src[i]);
 }
 
-static __be32 tb_crc(void *data, size_t len)
+static __be32 tb_crc(const void *data, size_t len)
 {
 	return cpu_to_be32(~__crc32c_le(~0, data, len));
 }
@@ -315,6 +420,7 @@ 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);
+	struct tb_cfg_request *req;
 	__be32 crc32;
 
 	if (canceled)
@@ -361,48 +467,135 @@ static void tb_ctl_rx_callback(struct tb_ring *ring, struct ring_frame *frame,
 		goto rx;
 
 	default:
-		tb_ctl_dbg(pkg->ctl, "RX: unknown package %#x, dropping\n",
-			   frame->eof);
-		goto rx;
+		break;
 	}
 
-	if (!kfifo_put(&pkg->ctl->response_fifo, pkg)) {
-		tb_ctl_err(pkg->ctl, "RX: fifo is full\n");
-		goto rx;
+	/*
+	 * The received packet will be processed only if there is an
+	 * active request and that the packet is what is expected. This
+	 * prevents packets such as replies coming after timeout has
+	 * triggered from messing with the active requests.
+	 */
+	req = tb_cfg_request_find(pkg->ctl, pkg);
+	if (req) {
+		if (req->copy(req, pkg))
+			schedule_work(&req->work);
+		tb_cfg_request_put(req);
 	}
-	complete(&pkg->ctl->response_ready);
-	return;
+
 rx:
 	tb_ctl_rx_submit(pkg);
 }
 
+static void tb_cfg_request_work(struct work_struct *work)
+{
+	struct tb_cfg_request *req = container_of(work, typeof(*req), work);
+
+	if (!test_bit(TB_CFG_REQUEST_CANCELED, &req->flags))
+		req->callback(req->callback_data);
+
+	tb_cfg_request_dequeue(req);
+	tb_cfg_request_put(req);
+}
+
 /**
- * tb_ctl_rx() - receive a packet from the control channel
+ * tb_cfg_request() - Start control request not waiting for it to complete
+ * @ctl: Control channel to use
+ * @req: Request to start
+ * @callback: Callback called when the request is completed
+ * @callback_data: Data to be passed to @callback
+ *
+ * This queues @req on the given control channel without waiting for it
+ * to complete. When the request completes @callback is called.
  */
-static struct tb_cfg_result tb_ctl_rx(struct tb_ctl *ctl, void *buffer,
-				      size_t length, int timeout_msec,
-				      u64 route, enum tb_cfg_pkg_type type)
+int tb_cfg_request(struct tb_ctl *ctl, struct tb_cfg_request *req,
+		   void (*callback)(void *), void *callback_data)
 {
-	struct tb_cfg_result res;
-	struct ctl_pkg *pkg;
+	int ret;
 
-	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 };
-	}
+	req->flags = 0;
+	req->callback = callback;
+	req->callback_data = callback_data;
+	INIT_WORK(&req->work, tb_cfg_request_work);
+	INIT_LIST_HEAD(&req->list);
 
-	res = parse_header(pkg, length, type, route);
-	if (!res.err)
-		memcpy(buffer, pkg->buffer, length);
-	tb_ctl_rx_submit(pkg);
-	return res;
+	tb_cfg_request_get(req);
+	ret = tb_cfg_request_enqueue(ctl, req);
+	if (ret)
+		goto err_put;
+
+	ret = tb_ctl_tx(ctl, req->request, req->request_size,
+			req->request_type);
+	if (ret)
+		goto err_dequeue;
+
+	if (!req->response)
+		schedule_work(&req->work);
+
+	return 0;
+
+err_dequeue:
+	tb_cfg_request_dequeue(req);
+err_put:
+	tb_cfg_request_put(req);
+
+	return ret;
+}
+
+/**
+ * tb_cfg_request_cancel() - Cancel a control request
+ * @req: Request to cancel
+ * @err: Error to assign to the request
+ *
+ * This function can be used to cancel ongoing request. It will wait
+ * until the request is not active anymore.
+ */
+void tb_cfg_request_cancel(struct tb_cfg_request *req, int err)
+{
+	set_bit(TB_CFG_REQUEST_CANCELED, &req->flags);
+	schedule_work(&req->work);
+	wait_event(tb_cfg_request_cancel_queue, !tb_cfg_request_is_active(req));
+	req->result.err = err;
 }
 
+static void tb_cfg_request_complete(void *data)
+{
+	complete(data);
+}
+
+/**
+ * tb_cfg_request_sync() - Start control request and wait until it completes
+ * @ctl: Control channel to use
+ * @req: Request to start
+ * @timeout_msec: Timeout how long to wait @req to complete
+ *
+ * Starts a control request and waits until it completes. If timeout
+ * triggers the request is canceled before function returns. Note the
+ * caller needs to make sure only one message for given switch is active
+ * at a time.
+ */
+struct tb_cfg_result tb_cfg_request_sync(struct tb_ctl *ctl,
+					 struct tb_cfg_request *req,
+					 int timeout_msec)
+{
+	unsigned long timeout = msecs_to_jiffies(timeout_msec);
+	struct tb_cfg_result res = { 0 };
+	DECLARE_COMPLETION_ONSTACK(done);
+	int ret;
+
+	ret = tb_cfg_request(ctl, req, tb_cfg_request_complete, &done);
+	if (ret) {
+		res.err = ret;
+		return res;
+	}
+
+	if (!wait_for_completion_timeout(&done, timeout))
+		tb_cfg_request_cancel(req, -ETIMEDOUT);
+
+	flush_work(&req->work);
+
+	return req->result;
+}
 
 /* public interface, alloc/start/stop/free */
 
@@ -423,8 +616,8 @@ struct tb_ctl *tb_ctl_alloc(struct tb_nhi *nhi, event_cb cb, void *cb_data)
 	ctl->callback = cb;
 	ctl->callback_data = cb_data;
 
-	init_completion(&ctl->response_ready);
-	INIT_KFIFO(ctl->response_fifo);
+	mutex_init(&ctl->request_queue_lock);
+	INIT_LIST_HEAD(&ctl->request_queue);
 	ctl->frame_pool = dma_pool_create("thunderbolt_ctl", &nhi->pdev->dev,
 					 TB_FRAME_SIZE, 4, 0);
 	if (!ctl->frame_pool)
@@ -492,6 +685,8 @@ void tb_ctl_start(struct tb_ctl *ctl)
 	ring_start(ctl->rx);
 	for (i = 0; i < TB_CTL_RX_PKG_COUNT; i++)
 		tb_ctl_rx_submit(ctl->rx_packets[i]);
+
+	ctl->running = true;
 }
 
 /**
@@ -504,12 +699,16 @@ void tb_ctl_start(struct tb_ctl *ctl)
  */
 void tb_ctl_stop(struct tb_ctl *ctl)
 {
+	mutex_lock(&ctl->request_queue_lock);
+	ctl->running = false;
+	mutex_unlock(&ctl->request_queue_lock);
+
 	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);
+	if (!list_empty(&ctl->request_queue))
+		tb_ctl_WARN(ctl, "dangling request in request_queue\n");
+	INIT_LIST_HEAD(&ctl->request_queue);
 	tb_ctl_info(ctl, "control channel stopped\n");
 }
 
@@ -532,6 +731,49 @@ int tb_cfg_error(struct tb_ctl *ctl, u64 route, u32 port,
 	return tb_ctl_tx(ctl, &pkg, sizeof(pkg), TB_CFG_PKG_ERROR);
 }
 
+static bool tb_cfg_match(const struct tb_cfg_request *req,
+			 const struct ctl_pkg *pkg)
+{
+	u64 route = tb_cfg_get_route(pkg->buffer) & ~BIT_ULL(63);
+
+	if (pkg->frame.eof == TB_CFG_PKG_ERROR)
+		return true;
+
+	if (pkg->frame.eof != req->response_type)
+		return false;
+	if (route != tb_cfg_get_route(req->request))
+		return false;
+	if (pkg->frame.size != req->response_size)
+		return false;
+
+	if (pkg->frame.eof == TB_CFG_PKG_READ ||
+	    pkg->frame.eof == TB_CFG_PKG_WRITE) {
+		const struct cfg_read_pkg *req_hdr = req->request;
+		const struct cfg_read_pkg *res_hdr = pkg->buffer;
+
+		if (req_hdr->addr.seq != res_hdr->addr.seq)
+			return false;
+	}
+
+	return true;
+}
+
+static bool tb_cfg_copy(struct tb_cfg_request *req, const struct ctl_pkg *pkg)
+{
+	struct tb_cfg_result res;
+
+	/* Now make sure it is in expected format */
+	res = parse_header(pkg, req->response_size, req->response_type,
+			   tb_cfg_get_route(req->request));
+	if (!res.err)
+		memcpy(req->response, pkg->buffer, req->response_size);
+
+	req->result = res;
+
+	/* Always complete when first response is received */
+	return true;
+}
+
 /**
  * tb_cfg_reset() - send a reset packet and wait for a response
  *
@@ -542,16 +784,31 @@ int tb_cfg_error(struct tb_ctl *ctl, u64 route, u32 port,
 struct tb_cfg_result tb_cfg_reset(struct tb_ctl *ctl, u64 route,
 				  int timeout_msec)
 {
-	int err;
 	struct cfg_reset_pkg request = { .header = tb_cfg_make_header(route) };
+	struct tb_cfg_result res = { 0 };
 	struct tb_cfg_header reply;
+	struct tb_cfg_request *req;
+
+	req = tb_cfg_request_alloc();
+	if (!req) {
+		res.err = -ENOMEM;
+		return res;
+	}
+
+	req->match = tb_cfg_match;
+	req->copy = tb_cfg_copy;
+	req->request = &request;
+	req->request_size = sizeof(request);
+	req->request_type = TB_CFG_PKG_RESET;
+	req->response = &reply;
+	req->response_size = sizeof(reply);
+	req->response_type = sizeof(TB_CFG_PKG_RESET);
+
+	res = tb_cfg_request_sync(ctl, req, timeout_msec);
 
-	err = tb_ctl_tx(ctl, &request, sizeof(request), TB_CFG_PKG_RESET);
-	if (err)
-		return (struct tb_cfg_result) { .err = err };
+	tb_cfg_request_put(req);
 
-	return tb_ctl_rx(ctl, &reply, sizeof(reply), timeout_msec, route,
-			 TB_CFG_PKG_RESET);
+	return res;
 }
 
 /**
@@ -574,13 +831,39 @@ struct tb_cfg_result tb_cfg_read_raw(struct tb_ctl *ctl, void *buffer,
 		},
 	};
 	struct cfg_write_pkg reply;
+	int retries = 0;
 
-	res.err = tb_ctl_tx(ctl, &request, sizeof(request), TB_CFG_PKG_READ);
-	if (res.err)
-		return res;
+	while (retries < TB_CTL_RETRIES) {
+		struct tb_cfg_request *req;
+
+		req = tb_cfg_request_alloc();
+		if (!req) {
+			res.err = -ENOMEM;
+			return res;
+		}
+
+		request.addr.seq = retries++;
+
+		req->match = tb_cfg_match;
+		req->copy = tb_cfg_copy;
+		req->request = &request;
+		req->request_size = sizeof(request);
+		req->request_type = TB_CFG_PKG_READ;
+		req->response = &reply;
+		req->response_size = 12 + 4 * length;
+		req->response_type = TB_CFG_PKG_READ;
+
+		res = tb_cfg_request_sync(ctl, req, timeout_msec);
+
+		tb_cfg_request_put(req);
+
+		if (res.err != -ETIMEDOUT)
+			break;
+
+		/* Wait a bit (arbitrary time) until we send a retry */
+		usleep_range(10, 100);
+	}
 
-	res = tb_ctl_rx(ctl, &reply, 12 + 4 * length, timeout_msec, route,
-			TB_CFG_PKG_READ);
 	if (res.err)
 		return res;
 
@@ -611,15 +894,41 @@ struct tb_cfg_result tb_cfg_write_raw(struct tb_ctl *ctl, const void *buffer,
 		},
 	};
 	struct cfg_read_pkg reply;
+	int retries = 0;
 
 	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;
+	while (retries < TB_CTL_RETRIES) {
+		struct tb_cfg_request *req;
+
+		req = tb_cfg_request_alloc();
+		if (!req) {
+			res.err = -ENOMEM;
+			return res;
+		}
+
+		request.addr.seq = retries++;
+
+		req->match = tb_cfg_match;
+		req->copy = tb_cfg_copy;
+		req->request = &request;
+		req->request_size = 12 + 4 * length;
+		req->request_type = TB_CFG_PKG_WRITE;
+		req->response = &reply;
+		req->response_size = sizeof(reply);
+		req->response_type = TB_CFG_PKG_WRITE;
+
+		res = tb_cfg_request_sync(ctl, req, timeout_msec);
+
+		tb_cfg_request_put(req);
+
+		if (res.err != -ETIMEDOUT)
+			break;
+
+		/* Wait a bit (arbitrary time) until we send a retry */
+		usleep_range(10, 100);
+	}
 
-	res = tb_ctl_rx(ctl, &reply, sizeof(reply), timeout_msec, route,
-			TB_CFG_PKG_WRITE);
 	if (res.err)
 		return res;
 
@@ -633,11 +942,25 @@ int tb_cfg_read(struct tb_ctl *ctl, void *buffer, u64 route, u32 port,
 {
 	struct tb_cfg_result res = tb_cfg_read_raw(ctl, buffer, route, port,
 			space, offset, length, TB_CFG_DEFAULT_TIMEOUT);
-	if (res.err == 1) {
+	switch (res.err) {
+	case 0:
+		/* Success */
+		break;
+
+	case 1:
+		/* Thunderbolt error, tb_error holds the actual number */
 		tb_cfg_print_error(ctl, &res);
 		return -EIO;
+
+	case -ETIMEDOUT:
+		tb_ctl_warn(ctl, "timeout reading config space %u from %#x\n",
+			    space, offset);
+		break;
+
+	default:
+		WARN(1, "tb_cfg_read: %d\n", res.err);
+		break;
 	}
-	WARN(res.err, "tb_cfg_read: %d\n", res.err);
 	return res.err;
 }
 
@@ -646,11 +969,25 @@ int tb_cfg_write(struct tb_ctl *ctl, const void *buffer, u64 route, u32 port,
 {
 	struct tb_cfg_result res = tb_cfg_write_raw(ctl, buffer, route, port,
 			space, offset, length, TB_CFG_DEFAULT_TIMEOUT);
-	if (res.err == 1) {
+	switch (res.err) {
+	case 0:
+		/* Success */
+		break;
+
+	case 1:
+		/* Thunderbolt error, tb_error holds the actual number */
 		tb_cfg_print_error(ctl, &res);
 		return -EIO;
+
+	case -ETIMEDOUT:
+		tb_ctl_warn(ctl, "timeout writing config space %u to %#x\n",
+			    space, offset);
+		break;
+
+	default:
+		WARN(1, "tb_cfg_write: %d\n", res.err);
+		break;
 	}
-	WARN(res.err, "tb_cfg_write: %d\n", res.err);
 	return res.err;
 }
 
diff --git a/drivers/thunderbolt/ctl.h b/drivers/thunderbolt/ctl.h
index 2b23e030a85b..36fd28b1c1c5 100644
--- a/drivers/thunderbolt/ctl.h
+++ b/drivers/thunderbolt/ctl.h
@@ -7,6 +7,8 @@
 #ifndef _TB_CFG
 #define _TB_CFG
 
+#include <linux/kref.h>
+
 #include "nhi.h"
 #include "tb_msgs.h"
 
@@ -39,6 +41,69 @@ struct tb_cfg_result {
 	enum tb_cfg_error tb_error; /* valid if err == 1 */
 };
 
+struct ctl_pkg {
+	struct tb_ctl *ctl;
+	void *buffer;
+	struct ring_frame frame;
+};
+
+/**
+ * struct tb_cfg_request - Control channel request
+ * @kref: Reference count
+ * @ctl: Pointer to the control channel structure. Only set when the
+ *	 request is queued.
+ * @request_size: Size of the request packet (in bytes)
+ * @request_type: Type of the request packet
+ * @response: Response is stored here
+ * @response_size: Maximum size of one response packet
+ * @response_type: Expected type of the response packet
+ * @npackets: Number of packets expected to be returned with this request
+ * @match: Function used to match the incoming packet
+ * @copy: Function used to copy the incoming packet to @response
+ * @callback: Callback called when the request is finished successfully
+ * @callback_data: Data to be passed to @callback
+ * @flags: Flags for the request
+ * @work: Work item used to complete the request
+ * @result: Result after the request has been completed
+ * @list: Requests are queued using this field
+ *
+ * An arbitrary request over Thunderbolt control channel. For standard
+ * control channel message, one should use tb_cfg_read/write() and
+ * friends if possible.
+ */
+struct tb_cfg_request {
+	struct kref kref;
+	struct tb_ctl *ctl;
+	const void *request;
+	size_t request_size;
+	enum tb_cfg_pkg_type request_type;
+	void *response;
+	size_t response_size;
+	enum tb_cfg_pkg_type response_type;
+	size_t npackets;
+	bool (*match)(const struct tb_cfg_request *req,
+		      const struct ctl_pkg *pkg);
+	bool (*copy)(struct tb_cfg_request *req, const struct ctl_pkg *pkg);
+	void (*callback)(void *callback_data);
+	void *callback_data;
+	unsigned long flags;
+	struct work_struct work;
+	struct tb_cfg_result result;
+	struct list_head list;
+};
+
+#define TB_CFG_REQUEST_ACTIVE		0
+#define TB_CFG_REQUEST_CANCELED		1
+
+struct tb_cfg_request *tb_cfg_request_alloc(void);
+void tb_cfg_request_get(struct tb_cfg_request *req);
+void tb_cfg_request_put(struct tb_cfg_request *req);
+int tb_cfg_request(struct tb_ctl *ctl, struct tb_cfg_request *req,
+		   void (*callback)(void *), void *callback_data);
+void tb_cfg_request_cancel(struct tb_cfg_request *req, int err);
+struct tb_cfg_result tb_cfg_request_sync(struct tb_ctl *ctl,
+			struct tb_cfg_request *req, int timeout_msec);
+
 static inline u64 tb_cfg_get_route(const struct tb_cfg_header *header)
 {
 	return (u64) header->route_hi << 32 | header->route_lo;
diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
index 5bb9a5d60d2c..98a405384596 100644
--- a/drivers/thunderbolt/tb.h
+++ b/drivers/thunderbolt/tb.h
@@ -132,7 +132,7 @@ struct tb_cm_ops {
 /**
  * struct tb - main thunderbolt bus structure
  * @dev: Domain device
- * @lock: Big lock. Must be held when accessing cfg or any struct
+ * @lock: Big lock. Must be held when accessing any struct
  *	  tb_switch / struct tb_port.
  * @nhi: Pointer to the NHI structure
  * @ctl: Control channel for this domain
-- 
2.11.0