drm/i915/guc: Implement response handling in send_ct()

Instead of returning small data in response status dword,
GuC may append longer data as response message payload.
If caller provides response buffer, we will copy received
data and use number of received data dwords as new success
return value. We will WARN if response from GuC does not
match caller expectation.

v2: fix timeout and checkpatch warnings (Michal)
v3: fix checkpatch again (Michel)
    update wait function name (Michal)
    no need for spinlock_irqsave (MichalWi)
    no magic numbers (MichalWi)
    must check before use (Jani)
    add some more documentation (Michal)
v4: update documentation (Michal)
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com> #2.5
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180327121439.70096-1-michal.wajdeczko@intel.com

drivers/gpu/drm/i915/intel_guc_ct.c

@@ -24,6 +24,14 @@
 #include "i915_drv.h"
 #include "intel_guc_ct.h"
 
+struct ct_request {
+	struct list_head link;
+	u32 fence;
+	u32 status;
+	u32 response_len;
+	u32 *response_buf;
+};
+
 enum { CTB_SEND = 0, CTB_RECV = 1 };
 
 enum { CTB_OWNER_HOST = 0 };
@@ -36,6 +44,9 @@ void intel_guc_ct_init_early(struct intel_guc_ct *ct)
 {
 	/* we're using static channel owners */
 	ct->host_channel.owner = CTB_OWNER_HOST;
+
+	spin_lock_init(&ct->lock);
+	INIT_LIST_HEAD(&ct->pending_requests);
 }
 
 static inline struct intel_guc *ct_to_guc(struct intel_guc_ct *ct)
@@ -294,7 +305,8 @@ static u32 ctch_get_next_fence(struct intel_guc_ct_channel *ctch)
 static int ctb_write(struct intel_guc_ct_buffer *ctb,
 		     const u32 *action,
 		     u32 len /* in dwords */,
-		     u32 fence)
+		     u32 fence,
+		     bool want_response)
 {
 	struct guc_ct_buffer_desc *desc = ctb->desc;
 	u32 head = desc->head / 4;	/* in dwords */
@@ -331,6 +343,7 @@ static int ctb_write(struct intel_guc_ct_buffer *ctb,
 	 */
 	header = (len << GUC_CT_MSG_LEN_SHIFT) |
 		 (GUC_CT_MSG_WRITE_FENCE_TO_DESC) |
+		 (want_response ? GUC_CT_MSG_SEND_STATUS : 0) |
 		 (action[0] << GUC_CT_MSG_ACTION_SHIFT);
 
 	cmds[tail] = header;
@@ -401,36 +414,108 @@ static int wait_for_ctb_desc_update(struct guc_ct_buffer_desc *desc,
 	return err;
 }
 
-static int ctch_send(struct intel_guc *guc,
+/**
+ * wait_for_ct_request_update - Wait for CT request state update.
+ * @req:	pointer to pending request
+ * @status:	placeholder for status
+ *
+ * For each sent request, Guc shall send bac CT response message.
+ * Our message handler will update status of tracked request once
+ * response message with given fence is received. Wait here and
+ * check for valid response status value.
+ *
+ * Return:
+ * *	0 response received (status is valid)
+ * *	-ETIMEDOUT no response within hardcoded timeout
+ */
+static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
+{
+	int err;
+
+	/*
+	 * Fast commands should complete in less than 10us, so sample quickly
+	 * up to that length of time, then switch to a slower sleep-wait loop.
+	 * No GuC command should ever take longer than 10ms.
+	 */
+#define done INTEL_GUC_MSG_IS_RESPONSE(READ_ONCE(req->status))
+	err = wait_for_us(done, 10);
+	if (err)
+		err = wait_for(done, 10);
+#undef done
+
+	if (unlikely(err))
+		DRM_ERROR("CT: fence %u err %d\n", req->fence, err);
+
+	*status = req->status;
+	return err;
+}
+
+static int ctch_send(struct intel_guc_ct *ct,
 		     struct intel_guc_ct_channel *ctch,
 		     const u32 *action,
 		     u32 len,
+		     u32 *response_buf,
+		     u32 response_buf_size,
 		     u32 *status)
 {
 	struct intel_guc_ct_buffer *ctb = &ctch->ctbs[CTB_SEND];
 	struct guc_ct_buffer_desc *desc = ctb->desc;
+	struct ct_request request;
+	unsigned long flags;
 	u32 fence;
 	int err;
 
 	GEM_BUG_ON(!ctch_is_open(ctch));
 	GEM_BUG_ON(!len);
 	GEM_BUG_ON(len & ~GUC_CT_MSG_LEN_MASK);
+	GEM_BUG_ON(!response_buf && response_buf_size);
 
 	fence = ctch_get_next_fence(ctch);
-	err = ctb_write(ctb, action, len, fence);
+	request.fence = fence;
+	request.status = 0;
+	request.response_len = response_buf_size;
+	request.response_buf = response_buf;
+
+	spin_lock_irqsave(&ct->lock, flags);
+	list_add_tail(&request.link, &ct->pending_requests);
+	spin_unlock_irqrestore(&ct->lock, flags);
+
+	err = ctb_write(ctb, action, len, fence, !!response_buf);
 	if (unlikely(err))
-		return err;
+		goto unlink;
 
-	intel_guc_notify(guc);
+	intel_guc_notify(ct_to_guc(ct));
 
+	if (response_buf)
+		err = wait_for_ct_request_update(&request, status);
+	else
 		err = wait_for_ctb_desc_update(desc, fence, status);
 	if (unlikely(err))
-		return err;
-	if (!INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(*status))
-		return -EIO;
+		goto unlink;
+
+	if (!INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(*status)) {
+		err = -EIO;
+		goto unlink;
+	}
 
-	/* Use data from the GuC status as our return value */
-	return INTEL_GUC_MSG_TO_DATA(*status);
+	if (response_buf) {
+		/* There shall be no data in the status */
+		WARN_ON(INTEL_GUC_MSG_TO_DATA(request.status));
+		/* Return actual response len */
+		err = request.response_len;
+	} else {
+		/* There shall be no response payload */
+		WARN_ON(request.response_len);
+		/* Return data decoded from the status dword */
+		err = INTEL_GUC_MSG_TO_DATA(*status);
+	}
+
+unlink:
+	spin_lock_irqsave(&ct->lock, flags);
+	list_del(&request.link);
+	spin_unlock_irqrestore(&ct->lock, flags);
+
+	return err;
 }
 
 /*
@@ -439,13 +524,15 @@ static int ctch_send(struct intel_guc *guc,
 static int intel_guc_send_ct(struct intel_guc *guc, const u32 *action, u32 len,
 			     u32 *response_buf, u32 response_buf_size)
 {
-	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
+	struct intel_guc_ct *ct = &guc->ct;
+	struct intel_guc_ct_channel *ctch = &ct->host_channel;
 	u32 status = ~0; /* undefined */
 	int ret;
 
 	mutex_lock(&guc->send_mutex);
 
-	ret = ctch_send(guc, ctch, action, len, &status);
+	ret = ctch_send(ct, ctch, action, len, response_buf, response_buf_size,
+			&status);
 	if (unlikely(ret < 0)) {
 		DRM_ERROR("CT: send action %#X failed; err=%d status=%#X\n",
 			  action[0], ret, status);
@@ -546,8 +633,12 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
 	u32 msglen = len + 1; /* total message length including header */
 	u32 fence;
 	u32 status;
+	u32 datalen;
+	struct ct_request *req;
+	bool found = false;
 
 	GEM_BUG_ON(!ct_header_is_response(header));
+	GEM_BUG_ON(!in_irq());
 
 	/* Response payload shall at least include fence and status */
 	if (unlikely(len < 2)) {
@@ -557,6 +648,7 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
 
 	fence = msg[1];
 	status = msg[2];
+	datalen = len - 2;
 
 	/* Format of the status follows RESPONSE message */
 	if (unlikely(!INTEL_GUC_MSG_IS_RESPONSE(status))) {
@@ -564,7 +656,29 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
 		return -EPROTO;
 	}
 
-	/* XXX */
+	spin_lock(&ct->lock);
+	list_for_each_entry(req, &ct->pending_requests, link) {
+		if (unlikely(fence != req->fence)) {
+			DRM_DEBUG_DRIVER("CT: request %u awaits response\n",
+					 req->fence);
+			continue;
+		}
+		if (unlikely(datalen > req->response_len)) {
+			DRM_ERROR("CT: response %u too long %*phn\n",
+				  req->fence, 4 * msglen, msg);
+			datalen = 0;
+		}
+		if (datalen)
+			memcpy(req->response_buf, msg + 3, 4 * datalen);
+		req->response_len = datalen;
+		WRITE_ONCE(req->status, status);
+		found = true;
+		break;
+	}
+	spin_unlock(&ct->lock);
+
+	if (!found)
+		DRM_ERROR("CT: unsolicited response %*phn\n", 4 * msglen, msg);
 	return 0;
 }
 

drivers/gpu/drm/i915/intel_guc_ct.h

@@ -75,6 +75,12 @@ struct intel_guc_ct_channel {
 struct intel_guc_ct {
 	struct intel_guc_ct_channel host_channel;
 	/* other channels are tbd */
+
+	/** @lock: protects pending requests list */
+	spinlock_t lock;
+
+	/** @pending_requests: list of requests waiting for response */
+	struct list_head pending_requests;
 };
 
 void intel_guc_ct_init_early(struct intel_guc_ct *ct);

drivers/gpu/drm/i915/intel_guc_fwif.h

@@ -327,6 +327,58 @@ struct guc_stage_desc {
 	u64 desc_private;
 } __packed;
 
+/**
+ * DOC: CTB based communication
+ *
+ * The CTB (command transport buffer) communication between Host and GuC
+ * is based on u32 data stream written to the shared buffer. One buffer can
+ * be used to transmit data only in one direction (one-directional channel).
+ *
+ * Current status of the each buffer is stored in the buffer descriptor.
+ * Buffer descriptor holds tail and head fields that represents active data
+ * stream. The tail field is updated by the data producer (sender), and head
+ * field is updated by the data consumer (receiver)::
+ *
+ *      +------------+
+ *      | DESCRIPTOR |          +=================+============+========+
+ *      +============+          |                 | MESSAGE(s) |        |
+ *      | address    |--------->+=================+============+========+
+ *      +------------+
+ *      | head       |          ^-----head--------^
+ *      +------------+
+ *      | tail       |          ^---------tail-----------------^
+ *      +------------+
+ *      | size       |          ^---------------size--------------------^
+ *      +------------+
+ *
+ * Each message in data stream starts with the single u32 treated as a header,
+ * followed by optional set of u32 data that makes message specific payload::
+ *
+ *      +------------+---------+---------+---------+
+ *      |         MESSAGE                          |
+ *      +------------+---------+---------+---------+
+ *      |   msg[0]   |   [1]   |   ...   |  [n-1]  |
+ *      +------------+---------+---------+---------+
+ *      |   MESSAGE  |       MESSAGE PAYLOAD       |
+ *      +   HEADER   +---------+---------+---------+
+ *      |            |    0    |   ...   |    n    |
+ *      +======+=====+=========+=========+=========+
+ *      | 31:16| code|         |         |         |
+ *      +------+-----+         |         |         |
+ *      |  15:5|flags|         |         |         |
+ *      +------+-----+         |         |         |
+ *      |   4:0|  len|         |         |         |
+ *      +------+-----+---------+---------+---------+
+ *
+ *                   ^-------------len-------------^
+ *
+ * The message header consists of:
+ *
+ * - **len**, indicates length of the message payload (in u32)
+ * - **code**, indicates message code
+ * - **flags**, holds various bits to control message handling
+ */
+
 /*
  * Describes single command transport buffer.
  * Used by both guc-master and clients.