drm/i915/guc: Cleanup adding GuC work items

We can just operate on the wq_tail directly (in the process descriptor).
This allows us to remove the duplicated tail from the client. While I'm
here let's also remove the constants kept in the client and document our
locking requirements. This causes a small change in one of GuC debugfs
files. We're no longer reporting constant values (which I don't think
is a problem), but we're also no longer reporting the tail (does anyone
care?).

v2: Update tail after wqi contents. (Chris)
v3: Really update tail after wqi contents.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170918092536.12287-1-michal.winiarski@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2447,8 +2447,6 @@ static void i915_guc_client_info(struct seq_file *m,
 		client->priority, client->stage_id, client->proc_desc_offset);
 	seq_printf(m, "\tDoorbell id %d, offset: 0x%lx\n",
 		client->doorbell_id, client->doorbell_offset);
-	seq_printf(m, "\tWQ size %d, offset: 0x%x, tail %d\n",
-		client->wq_size, client->wq_offset, client->wq_tail);
 
 	for_each_engine(engine, dev_priv, id) {
 		u64 submissions = client->submissions[id];

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -305,7 +305,7 @@ static void guc_proc_desc_init(struct intel_guc *guc,
 	desc->db_base_addr = 0;
 
 	desc->stage_id = client->stage_id;
-	desc->wq_size_bytes = client->wq_size;
+	desc->wq_size_bytes = GUC_WQ_SIZE;
 	desc->wq_status = WQ_STATUS_ACTIVE;
 	desc->priority = client->priority;
 }
@@ -390,8 +390,8 @@ static void guc_stage_desc_init(struct intel_guc *guc,
 	desc->db_trigger_cpu = (uintptr_t)__get_doorbell(client);
 	desc->db_trigger_uk = gfx_addr + client->doorbell_offset;
 	desc->process_desc = gfx_addr + client->proc_desc_offset;
-	desc->wq_addr = gfx_addr + client->wq_offset;
-	desc->wq_size = client->wq_size;
+	desc->wq_addr = gfx_addr + GUC_DB_SIZE;
+	desc->wq_size = GUC_WQ_SIZE;
 
 	desc->desc_private = (uintptr_t)client;
 }
@@ -416,14 +416,12 @@ static void guc_wq_item_append(struct i915_guc_client *client,
 	struct i915_gem_context *ctx = rq->ctx;
 	struct guc_process_desc *desc = __get_process_desc(client);
 	struct guc_wq_item *wqi;
-	u32 freespace, tail, wq_off;
+	u32 ring_tail, wq_off;
 
-	/* Free space is guaranteed */
-	freespace = CIRC_SPACE(client->wq_tail, desc->head, client->wq_size);
-	GEM_BUG_ON(freespace < wqi_size);
+	lockdep_assert_held(&client->wq_lock);
 
-	tail = intel_ring_set_tail(rq->ring, rq->tail) / sizeof(u64);
-	GEM_BUG_ON(tail > WQ_RING_TAIL_MAX);
+	ring_tail = intel_ring_set_tail(rq->ring, rq->tail) / sizeof(u64);
+	GEM_BUG_ON(ring_tail > WQ_RING_TAIL_MAX);
 
 	/* For now workqueue item is 4 DWs; workqueue buffer is 2 pages. So we
 	 * should not have the case where structure wqi is across page, neither
@@ -434,11 +432,11 @@ static void guc_wq_item_append(struct i915_guc_client *client,
 	 */
 	BUILD_BUG_ON(wqi_size != 16);
 
-	/* postincrement WQ tail for next time */
-	wq_off = client->wq_tail;
+	/* Free space is guaranteed. */
+	wq_off = READ_ONCE(desc->tail);
+	GEM_BUG_ON(CIRC_SPACE(wq_off, READ_ONCE(desc->head),
+			      GUC_WQ_SIZE) < wqi_size);
 	GEM_BUG_ON(wq_off & (wqi_size - 1));
-	client->wq_tail += wqi_size;
-	client->wq_tail &= client->wq_size - 1;
 
 	/* WQ starts from the page after doorbell / process_desc */
 	wqi = client->vaddr + wq_off + GUC_DB_SIZE;
@@ -451,8 +449,11 @@ static void guc_wq_item_append(struct i915_guc_client *client,
 
 	wqi->context_desc = lower_32_bits(intel_lr_context_descriptor(ctx, engine));
 
-	wqi->submit_element_info = tail << WQ_RING_TAIL_SHIFT;
+	wqi->submit_element_info = ring_tail << WQ_RING_TAIL_SHIFT;
 	wqi->fence_id = rq->global_seqno;
+
+	/* Postincrement WQ tail for next time. */
+	WRITE_ONCE(desc->tail, (wq_off + wqi_size) & (GUC_WQ_SIZE - 1));
 }
 
 static void guc_reset_wq(struct i915_guc_client *client)
@@ -461,18 +462,14 @@ static void guc_reset_wq(struct i915_guc_client *client)
 
 	desc->head = 0;
 	desc->tail = 0;
-
-	client->wq_tail = 0;
 }
 
 static void guc_ring_doorbell(struct i915_guc_client *client)
 {
-	struct guc_process_desc *desc = __get_process_desc(client);
 	struct guc_doorbell_info *db;
 	u32 cookie;
 
-	/* Update the tail so it is visible to GuC */
-	desc->tail = client->wq_tail;
+	lockdep_assert_held(&client->wq_lock);
 
 	/* pointer of current doorbell cacheline */
 	db = __get_doorbell(client);
@@ -812,8 +809,6 @@ guc_client_alloc(struct drm_i915_private *dev_priv,
 	client->engines = engines;
 	client->priority = priority;
 	client->doorbell_id = GUC_DOORBELL_INVALID;
-	client->wq_offset = GUC_DB_SIZE;
-	client->wq_size = GUC_WQ_SIZE;
 	spin_lock_init(&client->wq_lock);
 
 	ret = ida_simple_get(&guc->stage_ids, 0, GUC_MAX_STAGE_DESCRIPTORS,

drivers/gpu/drm/i915/intel_uc.h

@@ -68,10 +68,6 @@ struct i915_guc_client {
 	unsigned long doorbell_offset;
 
 	spinlock_t wq_lock;
-	uint32_t wq_offset;
-	uint32_t wq_size;
-	uint32_t wq_tail;
-
 	/* Per-engine counts of GuC submissions */
 	uint64_t submissions[I915_NUM_ENGINES];
 };