drm/i915: Unify intel_ring_begin()

Combine the near identical implementations of intel_logical_ring_begin()
and intel_ring_begin() - the only difference is that the logical wait
has to check for a matching ring (which is assumed by legacy).

In the process some debug messages are culled as there were following a
WARN if we hit an actual error.

v2: Updated commentary
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461833819-3991-12-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_lrc.c

@@ -721,48 +721,6 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 	return ret;
 }
 
-static int logical_ring_wait_for_space(struct drm_i915_gem_request *req,
-				       int bytes)
-{
-	struct intel_ringbuffer *ringbuf = req->ringbuf;
-	struct intel_engine_cs *engine = req->engine;
-	struct drm_i915_gem_request *target;
-	unsigned space;
-	int ret;
-
-	if (intel_ring_space(ringbuf) >= bytes)
-		return 0;
-
-	/* The whole point of reserving space is to not wait! */
-	WARN_ON(ringbuf->reserved_in_use);
-
-	list_for_each_entry(target, &engine->request_list, list) {
-		/*
-		 * The request queue is per-engine, so can contain requests
-		 * from multiple ringbuffers. Here, we must ignore any that
-		 * aren't from the ringbuffer we're considering.
-		 */
-		if (target->ringbuf != ringbuf)
-			continue;
-
-		/* Would completion of this request free enough space? */
-		space = __intel_ring_space(target->postfix, ringbuf->tail,
-					   ringbuf->size);
-		if (space >= bytes)
-			break;
-	}
-
-	if (WARN_ON(&target->list == &engine->request_list))
-		return -ENOSPC;
-
-	ret = i915_wait_request(target);
-	if (ret)
-		return ret;
-
-	ringbuf->space = space;
-	return 0;
-}
-
 /*
  * intel_logical_ring_advance_and_submit() - advance the tail and submit the workload
  * @request: Request to advance the logical ringbuffer of.
@@ -814,92 +772,6 @@ intel_logical_ring_advance_and_submit(struct drm_i915_gem_request *request)
 	return 0;
 }
 
-static void __wrap_ring_buffer(struct intel_ringbuffer *ringbuf)
-{
-	uint32_t __iomem *virt;
-	int rem = ringbuf->size - ringbuf->tail;
-
-	virt = ringbuf->virtual_start + ringbuf->tail;
-	rem /= 4;
-	while (rem--)
-		iowrite32(MI_NOOP, virt++);
-
-	ringbuf->tail = 0;
-	intel_ring_update_space(ringbuf);
-}
-
-static int logical_ring_prepare(struct drm_i915_gem_request *req, int bytes)
-{
-	struct intel_ringbuffer *ringbuf = req->ringbuf;
-	int remain_usable = ringbuf->effective_size - ringbuf->tail;
-	int remain_actual = ringbuf->size - ringbuf->tail;
-	int ret, total_bytes, wait_bytes = 0;
-	bool need_wrap = false;
-
-	if (ringbuf->reserved_in_use)
-		total_bytes = bytes;
-	else
-		total_bytes = bytes + ringbuf->reserved_size;
-
-	if (unlikely(bytes > remain_usable)) {
-		/*
-		 * Not enough space for the basic request. So need to flush
-		 * out the remainder and then wait for base + reserved.
-		 */
-		wait_bytes = remain_actual + total_bytes;
-		need_wrap = true;
-	} else {
-		if (unlikely(total_bytes > remain_usable)) {
-			/*
-			 * The base request will fit but the reserved space
-			 * falls off the end. So don't need an immediate wrap
-			 * and only need to effectively wait for the reserved
-			 * size space from the start of ringbuffer.
-			 */
-			wait_bytes = remain_actual + ringbuf->reserved_size;
-		} else if (total_bytes > ringbuf->space) {
-			/* No wrapping required, just waiting. */
-			wait_bytes = total_bytes;
-		}
-	}
-
-	if (wait_bytes) {
-		ret = logical_ring_wait_for_space(req, wait_bytes);
-		if (unlikely(ret))
-			return ret;
-
-		if (need_wrap)
-			__wrap_ring_buffer(ringbuf);
-	}
-
-	return 0;
-}
-
-/**
- * intel_logical_ring_begin() - prepare the logical ringbuffer to accept some commands
- *
- * @req: The request to start some new work for
- * @num_dwords: number of DWORDs that we plan to write to the ringbuffer.
- *
- * The ringbuffer might not be ready to accept the commands right away (maybe it needs to
- * be wrapped, or wait a bit for the tail to be updated). This function takes care of that
- * and also preallocates a request (every workload submission is still mediated through
- * requests, same as it did with legacy ringbuffer submission).
- *
- * Return: non-zero if the ringbuffer is not ready to be written to.
- */
-int intel_logical_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
-{
-	int ret;
-
-	ret = logical_ring_prepare(req, num_dwords * sizeof(uint32_t));
-	if (ret)
-		return ret;
-
-	req->ringbuf->space -= num_dwords * sizeof(uint32_t);
-	return 0;
-}
-
 int intel_logical_ring_reserve_space(struct drm_i915_gem_request *request)
 {
 	/*
@@ -912,7 +784,7 @@ int intel_logical_ring_reserve_space(struct drm_i915_gem_request *request)
 	 */
 	intel_ring_reserved_space_reserve(request->ringbuf, MIN_SPACE_FOR_ADD_REQUEST);
 
-	return intel_logical_ring_begin(request, 0);
+	return intel_ring_begin(request, 0);
 }
 
 /**
@@ -982,7 +854,7 @@ int intel_execlists_submission(struct i915_execbuffer_params *params,
 
 	if (engine == &dev_priv->engine[RCS] &&
 	    instp_mode != dev_priv->relative_constants_mode) {
-		ret = intel_logical_ring_begin(params->request, 4);
+		ret = intel_ring_begin(params->request, 4);
 		if (ret)
 			return ret;
 
@@ -1178,7 +1050,7 @@ static int intel_logical_ring_workarounds_emit(struct drm_i915_gem_request *req)
 	if (ret)
 		return ret;
 
-	ret = intel_logical_ring_begin(req, w->count * 2 + 2);
+	ret = intel_ring_begin(req, w->count * 2 + 2);
 	if (ret)
 		return ret;
 
@@ -1671,7 +1543,7 @@ static int intel_logical_ring_emit_pdps(struct drm_i915_gem_request *req)
 	const int num_lri_cmds = GEN8_LEGACY_PDPES * 2;
 	int i, ret;
 
-	ret = intel_logical_ring_begin(req, num_lri_cmds * 2 + 2);
+	ret = intel_ring_begin(req, num_lri_cmds * 2 + 2);
 	if (ret)
 		return ret;
 
@@ -1718,7 +1590,7 @@ static int gen8_emit_bb_start(struct drm_i915_gem_request *req,
 		req->ctx->ppgtt->pd_dirty_rings &= ~intel_engine_flag(req->engine);
 	}
 
-	ret = intel_logical_ring_begin(req, 4);
+	ret = intel_ring_begin(req, 4);
 	if (ret)
 		return ret;
 
@@ -1780,7 +1652,7 @@ static int gen8_emit_flush(struct drm_i915_gem_request *request,
 	uint32_t cmd;
 	int ret;
 
-	ret = intel_logical_ring_begin(request, 4);
+	ret = intel_ring_begin(request, 4);
 	if (ret)
 		return ret;
 
@@ -1848,7 +1720,7 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
 			vf_flush_wa = true;
 	}
 
-	ret = intel_logical_ring_begin(request, vf_flush_wa ? 12 : 6);
+	ret = intel_ring_begin(request, vf_flush_wa ? 12 : 6);
 	if (ret)
 		return ret;
 
@@ -1922,7 +1794,7 @@ static int gen8_emit_request(struct drm_i915_gem_request *request)
 	struct intel_ringbuffer *ringbuf = request->ringbuf;
 	int ret;
 
-	ret = intel_logical_ring_begin(request, 6 + WA_TAIL_DWORDS);
+	ret = intel_ring_begin(request, 6 + WA_TAIL_DWORDS);
 	if (ret)
 		return ret;
 
@@ -1946,7 +1818,7 @@ static int gen8_emit_request_render(struct drm_i915_gem_request *request)
 	struct intel_ringbuffer *ringbuf = request->ringbuf;
 	int ret;
 
-	ret = intel_logical_ring_begin(request, 8 + WA_TAIL_DWORDS);
+	ret = intel_ring_begin(request, 8 + WA_TAIL_DWORDS);
 	if (ret)
 		return ret;
 

drivers/gpu/drm/i915/intel_lrc.h

@@ -63,7 +63,6 @@ int intel_logical_ring_reserve_space(struct drm_i915_gem_request *request);
 void intel_logical_ring_stop(struct intel_engine_cs *engine);
 void intel_logical_ring_cleanup(struct intel_engine_cs *engine);
 int intel_logical_rings_init(struct drm_device *dev);
-int intel_logical_ring_begin(struct drm_i915_gem_request *req, int num_dwords);
 
 int logical_ring_flush_all_caches(struct drm_i915_gem_request *req);
 /**

drivers/gpu/drm/i915/intel_mocs.c

@@ -239,11 +239,9 @@ static int emit_mocs_control_table(struct drm_i915_gem_request *req,
 	if (WARN_ON(table->size > GEN9_NUM_MOCS_ENTRIES))
 		return -ENODEV;
 
-	ret = intel_logical_ring_begin(req, 2 + 2 * GEN9_NUM_MOCS_ENTRIES);
-	if (ret) {
-		DRM_DEBUG("intel_logical_ring_begin failed %d\n", ret);
+	ret = intel_ring_begin(req, 2 + 2 * GEN9_NUM_MOCS_ENTRIES);
+	if (ret)
 		return ret;
-	}
 
 	intel_logical_ring_emit(ringbuf,
 				MI_LOAD_REGISTER_IMM(GEN9_NUM_MOCS_ENTRIES));
@@ -305,11 +303,9 @@ static int emit_mocs_l3cc_table(struct drm_i915_gem_request *req,
 	if (WARN_ON(table->size > GEN9_NUM_MOCS_ENTRIES))
 		return -ENODEV;
 
-	ret = intel_logical_ring_begin(req, 2 + GEN9_NUM_MOCS_ENTRIES);
-	if (ret) {
-		DRM_DEBUG("intel_logical_ring_begin failed %d\n", ret);
+	ret = intel_ring_begin(req, 2 + GEN9_NUM_MOCS_ENTRIES);
+	if (ret)
 		return ret;
-	}
 
 	intel_logical_ring_emit(ringbuf,
 			MI_LOAD_REGISTER_IMM(GEN9_NUM_MOCS_ENTRIES / 2));

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -53,12 +53,6 @@ void intel_ring_update_space(struct intel_ringbuffer *ringbuf)
 					    ringbuf->tail, ringbuf->size);
 }
 
-int intel_ring_space(struct intel_ringbuffer *ringbuf)
-{
-	intel_ring_update_space(ringbuf);
-	return ringbuf->space;
-}
-
 bool intel_engine_stopped(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->dev->dev_private;
@@ -2325,51 +2319,6 @@ void intel_cleanup_engine(struct intel_engine_cs *engine)
 	engine->dev = NULL;
 }
 
-static int ring_wait_for_space(struct intel_engine_cs *engine, int n)
-{
-	struct intel_ringbuffer *ringbuf = engine->buffer;
-	struct drm_i915_gem_request *request;
-	unsigned space;
-	int ret;
-
-	if (intel_ring_space(ringbuf) >= n)
-		return 0;
-
-	/* The whole point of reserving space is to not wait! */
-	WARN_ON(ringbuf->reserved_in_use);
-
-	list_for_each_entry(request, &engine->request_list, list) {
-		space = __intel_ring_space(request->postfix, ringbuf->tail,
-					   ringbuf->size);
-		if (space >= n)
-			break;
-	}
-
-	if (WARN_ON(&request->list == &engine->request_list))
-		return -ENOSPC;
-
-	ret = i915_wait_request(request);
-	if (ret)
-		return ret;
-
-	ringbuf->space = space;
-	return 0;
-}
-
-static void __wrap_ring_buffer(struct intel_ringbuffer *ringbuf)
-{
-	uint32_t __iomem *virt;
-	int rem = ringbuf->size - ringbuf->tail;
-
-	virt = ringbuf->virtual_start + ringbuf->tail;
-	rem /= 4;
-	while (rem--)
-		iowrite32(MI_NOOP, virt++);
-
-	ringbuf->tail = 0;
-	intel_ring_update_space(ringbuf);
-}
-
 int intel_engine_idle(struct intel_engine_cs *engine)
 {
 	struct drm_i915_gem_request *req;
@@ -2411,62 +2360,81 @@ int intel_ring_reserve_space(struct drm_i915_gem_request *request)
 
 void intel_ring_reserved_space_reserve(struct intel_ringbuffer *ringbuf, int size)
 {
-	WARN_ON(ringbuf->reserved_size);
-	WARN_ON(ringbuf->reserved_in_use);
-
+	GEM_BUG_ON(ringbuf->reserved_size);
 	ringbuf->reserved_size = size;
 }
 
 void intel_ring_reserved_space_cancel(struct intel_ringbuffer *ringbuf)
 {
-	WARN_ON(ringbuf->reserved_in_use);
-
+	GEM_BUG_ON(!ringbuf->reserved_size);
 	ringbuf->reserved_size   = 0;
-	ringbuf->reserved_in_use = false;
 }
 
 void intel_ring_reserved_space_use(struct intel_ringbuffer *ringbuf)
 {
-	WARN_ON(ringbuf->reserved_in_use);
-
-	ringbuf->reserved_in_use = true;
-	ringbuf->reserved_tail   = ringbuf->tail;
+	GEM_BUG_ON(!ringbuf->reserved_size);
+	ringbuf->reserved_size   = 0;
 }
 
 void intel_ring_reserved_space_end(struct intel_ringbuffer *ringbuf)
 {
-	WARN_ON(!ringbuf->reserved_in_use);
-	if (ringbuf->tail > ringbuf->reserved_tail) {
-		WARN(ringbuf->tail > ringbuf->reserved_tail + ringbuf->reserved_size,
-		     "request reserved size too small: %d vs %d!\n",
-		     ringbuf->tail - ringbuf->reserved_tail, ringbuf->reserved_size);
-	} else {
+	GEM_BUG_ON(ringbuf->reserved_size);
+}
+
+static int wait_for_space(struct drm_i915_gem_request *req, int bytes)
+{
+	struct intel_ringbuffer *ringbuf = req->ringbuf;
+	struct intel_engine_cs *engine = req->engine;
+	struct drm_i915_gem_request *target;
+
+	intel_ring_update_space(ringbuf);
+	if (ringbuf->space >= bytes)
+		return 0;
+
 	/*
-		 * The ring was wrapped while the reserved space was in use.
-		 * That means that some unknown amount of the ring tail was
-		 * no-op filled and skipped. Thus simply adding the ring size
-		 * to the tail and doing the above space check will not work.
-		 * Rather than attempt to track how much tail was skipped,
-		 * it is much simpler to say that also skipping the sanity
-		 * check every once in a while is not a big issue.
+	 * Space is reserved in the ringbuffer for finalising the request,
+	 * as that cannot be allowed to fail. During request finalisation,
+	 * reserved_space is set to 0 to stop the overallocation and the
+	 * assumption is that then we never need to wait (which has the
+	 * risk of failing with EINTR).
+	 *
+	 * See also i915_gem_request_alloc() and i915_add_request().
 	 */
+	GEM_BUG_ON(!ringbuf->reserved_size);
+
+	list_for_each_entry(target, &engine->request_list, list) {
+		unsigned space;
+
+		/*
+		 * The request queue is per-engine, so can contain requests
+		 * from multiple ringbuffers. Here, we must ignore any that
+		 * aren't from the ringbuffer we're considering.
+		 */
+		if (target->ringbuf != ringbuf)
+			continue;
+
+		/* Would completion of this request free enough space? */
+		space = __intel_ring_space(target->postfix, ringbuf->tail,
+					   ringbuf->size);
+		if (space >= bytes)
+			break;
 	}
 
-	ringbuf->reserved_size   = 0;
-	ringbuf->reserved_in_use = false;
+	if (WARN_ON(&target->list == &engine->request_list))
+		return -ENOSPC;
+
+	return i915_wait_request(target);
 }
 
-static int __intel_ring_prepare(struct intel_engine_cs *engine, int bytes)
+int intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
 {
-	struct intel_ringbuffer *ringbuf = engine->buffer;
-	int remain_usable = ringbuf->effective_size - ringbuf->tail;
+	struct intel_ringbuffer *ringbuf = req->ringbuf;
 	int remain_actual = ringbuf->size - ringbuf->tail;
-	int ret, total_bytes, wait_bytes = 0;
+	int remain_usable = ringbuf->effective_size - ringbuf->tail;
+	int bytes = num_dwords * sizeof(u32);
+	int total_bytes, wait_bytes;
 	bool need_wrap = false;
 
-	if (ringbuf->reserved_in_use)
-		total_bytes = bytes;
-	else
 	total_bytes = bytes + ringbuf->reserved_size;
 
 	if (unlikely(bytes > remain_usable)) {
@@ -2476,44 +2444,40 @@ static int __intel_ring_prepare(struct intel_engine_cs *engine, int bytes)
 		 */
 		wait_bytes = remain_actual + total_bytes;
 		need_wrap = true;
-	} else {
-		if (unlikely(total_bytes > remain_usable)) {
+	} else if (unlikely(total_bytes > remain_usable)) {
 		/*
 		 * The base request will fit but the reserved space
-			 * falls off the end. So don't need an immediate wrap
+		 * falls off the end. So we don't need an immediate wrap
 		 * and only need to effectively wait for the reserved
 		 * size space from the start of ringbuffer.
 		 */
 		wait_bytes = remain_actual + ringbuf->reserved_size;
-		} else if (total_bytes > ringbuf->space) {
+	} else {
 		/* No wrapping required, just waiting. */
 		wait_bytes = total_bytes;
 	}
-	}
 
-	if (wait_bytes) {
-		ret = ring_wait_for_space(engine, wait_bytes);
+	if (wait_bytes > ringbuf->space) {
+		int ret = wait_for_space(req, wait_bytes);
 		if (unlikely(ret))
 			return ret;
 
-		if (need_wrap)
-			__wrap_ring_buffer(ringbuf);
+		intel_ring_update_space(ringbuf);
 	}
 
-	return 0;
-}
-
-int intel_ring_begin(struct drm_i915_gem_request *req,
-		     int num_dwords)
-{
-	struct intel_engine_cs *engine = req->engine;
-	int ret;
+	if (unlikely(need_wrap)) {
+		GEM_BUG_ON(remain_actual > ringbuf->space);
+		GEM_BUG_ON(ringbuf->tail + remain_actual > ringbuf->size);
 
-	ret = __intel_ring_prepare(engine, num_dwords * sizeof(uint32_t));
-	if (ret)
-		return ret;
+		/* Fill the tail with MI_NOOP */
+		memset(ringbuf->virtual_start + ringbuf->tail,
+		       0, remain_actual);
+		ringbuf->tail = 0;
+		ringbuf->space -= remain_actual;
+	}
 
-	engine->buffer->space -= num_dwords * sizeof(uint32_t);
+	ringbuf->space -= bytes;
+	GEM_BUG_ON(ringbuf->space < 0);
 	return 0;
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -108,8 +108,6 @@ struct intel_ringbuffer {
 	int size;
 	int effective_size;
 	int reserved_size;
-	int reserved_tail;
-	bool reserved_in_use;
 
 	/** We track the position of the requests in the ring buffer, and
 	 * when each is retired we increment last_retired_head as the GPU
@@ -459,7 +457,6 @@ static inline void intel_ring_advance(struct intel_engine_cs *engine)
 }
 int __intel_ring_space(int head, int tail, int size);
 void intel_ring_update_space(struct intel_ringbuffer *ringbuf);
-int intel_ring_space(struct intel_ringbuffer *ringbuf);
 bool intel_engine_stopped(struct intel_engine_cs *engine);
 
 int __must_check intel_engine_idle(struct intel_engine_cs *engine);