drm/i915: Simplify ELSP queue request tracking

Emulate HW to track and manage ELSP queue. A set of SW ports are defined
and requests are assigned to these ports before submitting them to HW. This
helps in cleaning up incomplete requests during reset recovery easier
especially after engine reset by decoupling elsp queue management. This
will become more clear in the next patch.

In the engine reset case we want to resume where we left-off after skipping
the incomplete batch which requires checking the elsp queue, removing
element and fixing elsp_submitted counts in some cases. Instead of directly
manipulating the elsp queue from reset path we can examine these ports, fix
up ringbuffer pointers using the incomplete request and restart submissions
again after reset.

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1470414607-32453-3-git-send-email-arun.siluvery@linux.intel.com
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160909131201.16673-6-chris@chris-wilson.co.uk

1 files changed, 168 insertions, 234 deletions

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7bb743f79d18..a33687d294b5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -156,6 +156,11 @@
 #define GEN8_CTX_STATUS_COMPLETE	(1 << 4)
 #define GEN8_CTX_STATUS_LITE_RESTORE	(1 << 15)
 
+#define GEN8_CTX_STATUS_COMPLETED_MASK \
+	 (GEN8_CTX_STATUS_ACTIVE_IDLE | \
+	  GEN8_CTX_STATUS_PREEMPTED | \
+	  GEN8_CTX_STATUS_ELEMENT_SWITCH)
+
 #define CTX_LRI_HEADER_0		0x01
 #define CTX_CONTEXT_CONTROL		0x02
 #define CTX_RING_HEAD			0x04
@@ -263,12 +268,10 @@ logical_ring_init_platform_invariants(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 
-	if (IS_GEN8(dev_priv) || IS_GEN9(dev_priv))
-		engine->idle_lite_restore_wa = ~0;
-
-	engine->disable_lite_restore_wa = (IS_SKL_REVID(dev_priv, 0, SKL_REVID_B0) ||
-					IS_BXT_REVID(dev_priv, 0, BXT_REVID_A1)) &&
-					(engine->id == VCS || engine->id == VCS2);
+	engine->disable_lite_restore_wa =
+		(IS_SKL_REVID(dev_priv, 0, SKL_REVID_B0) ||
+		 IS_BXT_REVID(dev_priv, 0, BXT_REVID_A1)) &&
+		(engine->id == VCS || engine->id == VCS2);
 
 	engine->ctx_desc_template = GEN8_CTX_VALID;
 	if (IS_GEN8(dev_priv))
@@ -351,11 +354,11 @@ execlists_update_context_pdps(struct i915_hw_ppgtt *ppgtt, u32 *reg_state)
 	ASSIGN_CTX_PDP(ppgtt, reg_state, 0);
 }
 
-static void execlists_update_context(struct drm_i915_gem_request *rq)
+static u64 execlists_update_context(struct drm_i915_gem_request *rq)
 {
-	struct intel_engine_cs *engine = rq->engine;
+	struct intel_context *ce = &rq->ctx->engine[rq->engine->id];
 	struct i915_hw_ppgtt *ppgtt = rq->ctx->ppgtt;
-	uint32_t *reg_state = rq->ctx->engine[engine->id].lrc_reg_state;
+	u32 *reg_state = ce->lrc_reg_state;
 
 	reg_state[CTX_RING_TAIL+1] = intel_ring_offset(rq->ring, rq->tail);
 
@@ -366,26 +369,34 @@ static void execlists_update_context(struct drm_i915_gem_request *rq)
 	 */
 	if (ppgtt && !USES_FULL_48BIT_PPGTT(ppgtt->base.dev))
 		execlists_update_context_pdps(ppgtt, reg_state);
+
+	return ce->lrc_desc;
 }
 
-static void execlists_elsp_write(struct drm_i915_gem_request *rq0,
-				 struct drm_i915_gem_request *rq1)
+static void execlists_submit_ports(struct intel_engine_cs *engine)
 {
-	struct intel_engine_cs *engine = rq0->engine;
-	struct drm_i915_private *dev_priv = rq0->i915;
+	struct drm_i915_private *dev_priv = engine->i915;
+	struct execlist_port *port = engine->execlist_port;
 	u32 __iomem *elsp =
 		dev_priv->regs + i915_mmio_reg_offset(RING_ELSP(engine));
 	u64 desc[2];
 
-	if (rq1) {
-		desc[1] = intel_lr_context_descriptor(rq1->ctx, rq1->engine);
-		rq1->elsp_submitted++;
+	if (!port[0].count)
+		execlists_context_status_change(port[0].request,
+						INTEL_CONTEXT_SCHEDULE_IN);
+	desc[0] = execlists_update_context(port[0].request);
+	engine->preempt_wa = port[0].count++; /* bdw only? fixed on skl? */
+
+	if (port[1].request) {
+		GEM_BUG_ON(port[1].count);
+		execlists_context_status_change(port[1].request,
+						INTEL_CONTEXT_SCHEDULE_IN);
+		desc[1] = execlists_update_context(port[1].request);
+		port[1].count = 1;
 	} else {
 		desc[1] = 0;
 	}
-
-	desc[0] = intel_lr_context_descriptor(rq0->ctx, rq0->engine);
-	rq0->elsp_submitted++;
+	GEM_BUG_ON(desc[0] == desc[1]);
 
 	/* You must always write both descriptors in the order below. */
 	writel(upper_32_bits(desc[1]), elsp);
@@ -396,141 +407,125 @@ static void execlists_elsp_write(struct drm_i915_gem_request *rq0,
 	writel(lower_32_bits(desc[0]), elsp);
 }
 
-static void execlists_elsp_submit_contexts(struct drm_i915_gem_request *rq0,
-					   struct drm_i915_gem_request *rq1)
+static bool ctx_single_port_submission(const struct i915_gem_context *ctx)
 {
-	struct drm_i915_private *dev_priv = rq0->i915;
-	unsigned int fw_domains = rq0->engine->fw_domains;
-
-	execlists_update_context(rq0);
-
-	if (rq1)
-		execlists_update_context(rq1);
+	return (IS_ENABLED(CONFIG_DRM_I915_GVT) &&
+		ctx->execlists_force_single_submission);
+}
 
-	spin_lock_irq(&dev_priv->uncore.lock);
-	intel_uncore_forcewake_get__locked(dev_priv, fw_domains);
+static bool can_merge_ctx(const struct i915_gem_context *prev,
+			  const struct i915_gem_context *next)
+{
+	if (prev != next)
+		return false;
 
-	execlists_elsp_write(rq0, rq1);
+	if (ctx_single_port_submission(prev))
+		return false;
 
-	intel_uncore_forcewake_put__locked(dev_priv, fw_domains);
-	spin_unlock_irq(&dev_priv->uncore.lock);
+	return true;
 }
 
-static void execlists_unqueue(struct intel_engine_cs *engine)
+static void execlists_dequeue(struct intel_engine_cs *engine)
 {
-	struct drm_i915_gem_request *req0 = NULL, *req1 = NULL;
-	struct drm_i915_gem_request *cursor, *tmp;
+	struct drm_i915_gem_request *cursor, *last;
+	struct execlist_port *port = engine->execlist_port;
+	bool submit = false;
+
+	last = port->request;
+	if (last)
+		/* WaIdleLiteRestore:bdw,skl
+		 * Apply the wa NOOPs to prevent ring:HEAD == req:TAIL
+		 * as we resubmit the request. See gen8_emit_request()
+		 * for where we prepare the padding after the end of the
+		 * request.
+		 */
+		last->tail = last->wa_tail;
 
-	assert_spin_locked(&engine->execlist_lock);
+	GEM_BUG_ON(port[1].request);
 
-	/*
-	 * If irqs are not active generate a warning as batches that finish
-	 * without the irqs may get lost and a GPU Hang may occur.
+	/* Hardware submission is through 2 ports. Conceptually each port
+	 * has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
+	 * static for a context, and unique to each, so we only execute
+	 * requests belonging to a single context from each ring. RING_HEAD
+	 * is maintained by the CS in the context image, it marks the place
+	 * where it got up to last time, and through RING_TAIL we tell the CS
+	 * where we want to execute up to this time.
+	 *
+	 * In this list the requests are in order of execution. Consecutive
+	 * requests from the same context are adjacent in the ringbuffer. We
+	 * can combine these requests into a single RING_TAIL update:
+	 *
+	 *              RING_HEAD...req1...req2
+	 *                                    ^- RING_TAIL
+	 * since to execute req2 the CS must first execute req1.
+	 *
+	 * Our goal then is to point each port to the end of a consecutive
+	 * sequence of requests as being the most optimal (fewest wake ups
+	 * and context switches) submission.
 	 */
-	WARN_ON(!intel_irqs_enabled(engine->i915));
-
-	/* Try to read in pairs */
-	list_for_each_entry_safe(cursor, tmp, &engine->execlist_queue,
-				 execlist_link) {
-		if (!req0) {
-			req0 = cursor;
-		} else if (req0->ctx == cursor->ctx) {
-			/* Same ctx: ignore first request, as second request
-			 * will update tail past first request's workload */
-			cursor->elsp_submitted = req0->elsp_submitted;
-			list_del(&req0->execlist_link);
-			i915_gem_request_put(req0);
-			req0 = cursor;
-		} else {
-			if (IS_ENABLED(CONFIG_DRM_I915_GVT)) {
-				/*
-				 * req0 (after merged) ctx requires single
-				 * submission, stop picking
-				 */
-				if (req0->ctx->execlists_force_single_submission)
-					break;
-				/*
-				 * req0 ctx doesn't require single submission,
-				 * but next req ctx requires, stop picking
-				 */
-				if (cursor->ctx->execlists_force_single_submission)
-					break;
-			}
-			req1 = cursor;
-			WARN_ON(req1->elsp_submitted);
-			break;
-		}
-	}
 
-	if (unlikely(!req0))
-		return;
-
-	execlists_context_status_change(req0, INTEL_CONTEXT_SCHEDULE_IN);
-
-	if (req1)
-		execlists_context_status_change(req1,
-						INTEL_CONTEXT_SCHEDULE_IN);
-
-	if (req0->elsp_submitted & engine->idle_lite_restore_wa) {
-		/*
-		 * WaIdleLiteRestore: make sure we never cause a lite restore
-		 * with HEAD==TAIL.
+	spin_lock(&engine->execlist_lock);
+	list_for_each_entry(cursor, &engine->execlist_queue, execlist_link) {
+		/* Can we combine this request with the current port? It has to
+		 * be the same context/ringbuffer and not have any exceptions
+		 * (e.g. GVT saying never to combine contexts).
 		 *
-		 * Apply the wa NOOPS to prevent ring:HEAD == req:TAIL as we
-		 * resubmit the request. See gen8_emit_request() for where we
-		 * prepare the padding after the end of the request.
+		 * If we can combine the requests, we can execute both by
+		 * updating the RING_TAIL to point to the end of the second
+		 * request, and so we never need to tell the hardware about
+		 * the first.
 		 */
-		req0->tail = req0->wa_tail;
+		if (last && !can_merge_ctx(cursor->ctx, last->ctx)) {
+			/* If we are on the second port and cannot combine
+			 * this request with the last, then we are done.
+			 */
+			if (port != engine->execlist_port)
+				break;
+
+			/* If GVT overrides us we only ever submit port[0],
+			 * leaving port[1] empty. Note that we also have
+			 * to be careful that we don't queue the same
+			 * context (even though a different request) to
+			 * the second port.
+			 */
+			if (ctx_single_port_submission(cursor->ctx))
+				break;
+
+			GEM_BUG_ON(last->ctx == cursor->ctx);
+
+			i915_gem_request_assign(&port->request, last);
+			port++;
+		}
+		last = cursor;
+		submit = true;
+	}
+	if (submit) {
+		/* Decouple all the requests submitted from the queue */
+		engine->execlist_queue.next = &cursor->execlist_link;
+		cursor->execlist_link.prev = &engine->execlist_queue;
+
+		i915_gem_request_assign(&port->request, last);
 	}
+	spin_unlock(&engine->execlist_lock);
 
-	execlists_elsp_submit_contexts(req0, req1);
+	if (submit)
+		execlists_submit_ports(engine);
 }
 
-static unsigned int
-execlists_check_remove_request(struct intel_engine_cs *engine, u32 ctx_id)
+static bool execlists_elsp_idle(struct intel_engine_cs *engine)
 {
-	struct drm_i915_gem_request *head_req;
-
-	assert_spin_locked(&engine->execlist_lock);
-
-	head_req = list_first_entry_or_null(&engine->execlist_queue,
-					    struct drm_i915_gem_request,
-					    execlist_link);
-
-	if (WARN_ON(!head_req || (head_req->ctx_hw_id != ctx_id)))
-               return 0;
-
-	WARN(head_req->elsp_submitted == 0, "Never submitted head request\n");
-
-	if (--head_req->elsp_submitted > 0)
-		return 0;
-
-	execlists_context_status_change(head_req, INTEL_CONTEXT_SCHEDULE_OUT);
-
-	list_del(&head_req->execlist_link);
-	i915_gem_request_put(head_req);
-
-	return 1;
+	return !engine->execlist_port[0].request;
 }
 
-static u32
-get_context_status(struct intel_engine_cs *engine, unsigned int read_pointer,
-		   u32 *context_id)
+static bool execlists_elsp_ready(struct intel_engine_cs *engine)
 {
-	struct drm_i915_private *dev_priv = engine->i915;
-	u32 status;
-
-	read_pointer %= GEN8_CSB_ENTRIES;
-
-	status = I915_READ_FW(RING_CONTEXT_STATUS_BUF_LO(engine, read_pointer));
-
-	if (status & GEN8_CTX_STATUS_IDLE_ACTIVE)
-		return 0;
+	int port;
 
-	*context_id = I915_READ_FW(RING_CONTEXT_STATUS_BUF_HI(engine,
-							      read_pointer));
+	port = 1; /* wait for a free slot */
+	if (engine->disable_lite_restore_wa || engine->preempt_wa)
+		port = 0; /* wait for GPU to be idle before continuing */
 
-	return status;
+	return !engine->execlist_port[port].request;
 }
 
 /*
@@ -540,67 +535,56 @@ get_context_status(struct intel_engine_cs *engine, unsigned int read_pointer,
 static void intel_lrc_irq_handler(unsigned long data)
 {
 	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
+	struct execlist_port *port = engine->execlist_port;
 	struct drm_i915_private *dev_priv = engine->i915;
-	u32 status_pointer;
-	unsigned int read_pointer, write_pointer;
-	u32 csb[GEN8_CSB_ENTRIES][2];
-	unsigned int csb_read = 0, i;
-	unsigned int submit_contexts = 0;
 
 	intel_uncore_forcewake_get(dev_priv, engine->fw_domains);
 
-	status_pointer = I915_READ_FW(RING_CONTEXT_STATUS_PTR(engine));
-
-	read_pointer = engine->next_context_status_buffer;
-	write_pointer = GEN8_CSB_WRITE_PTR(status_pointer);
-	if (read_pointer > write_pointer)
-		write_pointer += GEN8_CSB_ENTRIES;
-
-	while (read_pointer < write_pointer) {
-		if (WARN_ON_ONCE(csb_read == GEN8_CSB_ENTRIES))
-			break;
-		csb[csb_read][0] = get_context_status(engine, ++read_pointer,
-						      &csb[csb_read][1]);
-		csb_read++;
-	}
-
-	engine->next_context_status_buffer = write_pointer % GEN8_CSB_ENTRIES;
-
-	/* Update the read pointer to the old write pointer. Manual ringbuffer
-	 * management ftw </sarcasm> */
-	I915_WRITE_FW(RING_CONTEXT_STATUS_PTR(engine),
-		      _MASKED_FIELD(GEN8_CSB_READ_PTR_MASK,
-				    engine->next_context_status_buffer << 8));
-
-	intel_uncore_forcewake_put(dev_priv, engine->fw_domains);
-
-	spin_lock(&engine->execlist_lock);
+	if (!execlists_elsp_idle(engine)) {
+		u32 __iomem *csb_mmio =
+			dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine));
+		u32 __iomem *buf =
+			dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0));
+		unsigned int csb, head, tail;
+
+		csb = readl(csb_mmio);
+		head = GEN8_CSB_READ_PTR(csb);
+		tail = GEN8_CSB_WRITE_PTR(csb);
+		if (tail < head)
+			tail += GEN8_CSB_ENTRIES;
+		while (head < tail) {
+			unsigned int idx = ++head % GEN8_CSB_ENTRIES;
+			unsigned int status = readl(buf + 2 * idx);
+
+			if (!(status & GEN8_CTX_STATUS_COMPLETED_MASK))
+				continue;
+
+			GEM_BUG_ON(port[0].count == 0);
+			if (--port[0].count == 0) {
+				GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
+				execlists_context_status_change(port[0].request,
+								INTEL_CONTEXT_SCHEDULE_OUT);
+
+				i915_gem_request_put(port[0].request);
+				port[0] = port[1];
+				memset(&port[1], 0, sizeof(port[1]));
+
+				engine->preempt_wa = false;
+			}
 
-	for (i = 0; i < csb_read; i++) {
-		if (unlikely(csb[i][0] & GEN8_CTX_STATUS_PREEMPTED)) {
-			if (csb[i][0] & GEN8_CTX_STATUS_LITE_RESTORE) {
-				if (execlists_check_remove_request(engine, csb[i][1]))
-					WARN(1, "Lite Restored request removed from queue\n");
-			} else
-				WARN(1, "Preemption without Lite Restore\n");
+			GEM_BUG_ON(port[0].count == 0 &&
+				   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
 		}
 
-		if (csb[i][0] & (GEN8_CTX_STATUS_ACTIVE_IDLE |
-		    GEN8_CTX_STATUS_ELEMENT_SWITCH))
-			submit_contexts +=
-				execlists_check_remove_request(engine, csb[i][1]);
+		writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK,
+				     GEN8_CSB_WRITE_PTR(csb) << 8),
+		       csb_mmio);
 	}
 
-	if (submit_contexts) {
-		if (!engine->disable_lite_restore_wa ||
-		    (csb[i][0] & GEN8_CTX_STATUS_ACTIVE_IDLE))
-			execlists_unqueue(engine);
-	}
+	if (execlists_elsp_ready(engine))
+		execlists_dequeue(engine);
 
-	spin_unlock(&engine->execlist_lock);
-
-	if (unlikely(submit_contexts > 2))
-		DRM_ERROR("More than two context complete events?\n");
+	intel_uncore_forcewake_put(dev_priv, engine->fw_domains);
 }
 
 static void execlists_submit_request(struct drm_i915_gem_request *request)
@@ -609,12 +593,9 @@ static void execlists_submit_request(struct drm_i915_gem_request *request)
 
 	spin_lock_bh(&engine->execlist_lock);
 
-	i915_gem_request_get(request);
-	request->ctx_hw_id = request->ctx->hw_id;
-
-	if (list_empty(&engine->execlist_queue))
-		tasklet_hi_schedule(&engine->irq_tasklet);
 	list_add_tail(&request->execlist_link, &engine->execlist_queue);
+	if (execlists_elsp_idle(engine))
+		tasklet_hi_schedule(&engine->irq_tasklet);
 
 	spin_unlock_bh(&engine->execlist_lock);
 }
@@ -721,23 +702,6 @@ intel_logical_ring_advance(struct drm_i915_gem_request *request)
 	return 0;
 }
 
-void intel_execlists_cancel_requests(struct intel_engine_cs *engine)
-{
-	struct drm_i915_gem_request *req, *tmp;
-	LIST_HEAD(cancel_list);
-
-	WARN_ON(!mutex_is_locked(&engine->i915->drm.struct_mutex));
-
-	spin_lock_bh(&engine->execlist_lock);
-	list_replace_init(&engine->execlist_queue, &cancel_list);
-	spin_unlock_bh(&engine->execlist_lock);
-
-	list_for_each_entry_safe(req, tmp, &cancel_list, execlist_link) {
-		list_del(&req->execlist_link);
-		i915_gem_request_put(req);
-	}
-}
-
 static int intel_lr_context_pin(struct i915_gem_context *ctx,
 				struct intel_engine_cs *engine)
 {
@@ -1258,7 +1222,6 @@ static void lrc_init_hws(struct intel_engine_cs *engine)
 static int gen8_init_common_ring(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
-	unsigned int next_context_status_buffer_hw;
 
 	lrc_init_hws(engine);
 
@@ -1269,32 +1232,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
 	I915_WRITE(RING_MODE_GEN7(engine),
 		   _MASKED_BIT_DISABLE(GFX_REPLAY_MODE) |
 		   _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE));
-	POSTING_READ(RING_MODE_GEN7(engine));
-
-	/*
-	 * Instead of resetting the Context Status Buffer (CSB) read pointer to
-	 * zero, we need to read the write pointer from hardware and use its
-	 * value because "this register is power context save restored".
-	 * Effectively, these states have been observed:
-	 *
-	 *      | Suspend-to-idle (freeze) | Suspend-to-RAM (mem) |
-	 * BDW  | CSB regs not reset       | CSB regs reset       |
-	 * CHT  | CSB regs not reset       | CSB regs not reset   |
-	 * SKL  |         ?                |         ?            |
-	 * BXT  |         ?                |         ?            |
-	 */
-	next_context_status_buffer_hw =
-		GEN8_CSB_WRITE_PTR(I915_READ(RING_CONTEXT_STATUS_PTR(engine)));
 
-	/*
-	 * When the CSB registers are reset (also after power-up / gpu reset),
-	 * CSB write pointer is set to all 1's, which is not valid, use '5' in
-	 * this special case, so the first element read is CSB[0].
-	 */
-	if (next_context_status_buffer_hw == GEN8_CSB_PTR_MASK)
-		next_context_status_buffer_hw = (GEN8_CSB_ENTRIES - 1);
-
-	engine->next_context_status_buffer = next_context_status_buffer_hw;
 	DRM_DEBUG_DRIVER("Execlists enabled for %s\n", engine->name);
 
 	intel_engine_init_hangcheck(engine);
@@ -1680,10 +1618,6 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *engine)
 	}
 	intel_lr_context_unpin(dev_priv->kernel_context, engine);
 
-	engine->idle_lite_restore_wa = 0;
-	engine->disable_lite_restore_wa = false;
-	engine->ctx_desc_template = 0;
-
 	lrc_destroy_wa_ctx_obj(engine);
 	engine->i915 = NULL;
 }