drm/i915: Rearrange switch_context to load the aliasing ppgtt on first use

The code to switch_mm() is already handled by i915_switch_context(), the
only difference required to setup the aliasing ppgtt is that we need to
emit te switch_mm() on the first context, i.e. when transitioning from
engine->last_context == NULL. This allows us to defer the
initialisation of the GPU from early device initialisation to first use,
which should marginally speed up both. The caveat is that we then defer
the context initialisation until first use - i.e. we cannot assume that
the GPU engines are initialised. For example, this means that power
contexts for rc6 (Ironlake) need to explicitly loaded, as they are.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461833819-3991-11-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -3296,7 +3296,6 @@ void i915_gem_context_lost(struct drm_i915_private *dev_priv);
 void i915_gem_context_fini(struct drm_device *dev);
 void i915_gem_context_reset(struct drm_device *dev);
 int i915_gem_context_open(struct drm_device *dev, struct drm_file *file);
-int i915_gem_context_enable(struct drm_i915_gem_request *req);
 void i915_gem_context_close(struct drm_device *dev, struct drm_file *file);
 int i915_switch_context(struct drm_i915_gem_request *req);
 struct intel_context *

drivers/gpu/drm/i915/i915_gem.c

@@ -4911,36 +4911,6 @@ i915_gem_init_hw(struct drm_device *dev)
 	 * on re-initialisation
 	 */
 	ret = i915_gem_set_seqno(dev, dev_priv->next_seqno+0x100);
-	if (ret)
-		goto out;
-
-	/* Now it is safe to go back round and do everything else: */
-	for_each_engine(engine, dev_priv) {
-		struct drm_i915_gem_request *req;
-
-		req = i915_gem_request_alloc(engine, NULL);
-		if (IS_ERR(req)) {
-			ret = PTR_ERR(req);
-			break;
-		}
-
-		ret = i915_ppgtt_init_ring(req);
-		if (ret)
-			goto err_request;
-
-		ret = i915_gem_context_enable(req);
-		if (ret)
-			goto err_request;
-
-err_request:
-		i915_add_request_no_flush(req);
-		if (ret) {
-			DRM_ERROR("Failed to enable %s, error=%d\n",
-				  engine->name, ret);
-			i915_gem_cleanup_engines(dev);
-			break;
-		}
-	}
 
 out:
 	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);

drivers/gpu/drm/i915/i915_gem_context.c

@@ -431,27 +431,6 @@ void i915_gem_context_fini(struct drm_device *dev)
 	dev_priv->kernel_context = NULL;
 }
 
-int i915_gem_context_enable(struct drm_i915_gem_request *req)
-{
-	struct intel_engine_cs *engine = req->engine;
-	int ret;
-
-	if (i915.enable_execlists) {
-		if (engine->init_context == NULL)
-			return 0;
-
-		ret = engine->init_context(req);
-	} else
-		ret = i915_switch_context(req);
-
-	if (ret) {
-		DRM_ERROR("ring init context: %d\n", ret);
-		return ret;
-	}
-
-	return 0;
-}
-
 static int context_idr_cleanup(int id, void *p, void *data)
 {
 	struct intel_context *ctx = p;
@@ -630,7 +609,8 @@ static int remap_l3(struct drm_i915_gem_request *req, int slice)
 	return 0;
 }
 
-static inline bool skip_rcs_switch(struct intel_engine_cs *engine,
+static inline bool skip_rcs_switch(struct i915_hw_ppgtt *ppgtt,
+				   struct intel_engine_cs *engine,
 				   struct intel_context *to)
 {
 	if (to->remap_slice)
@@ -639,21 +619,27 @@ static inline bool skip_rcs_switch(struct intel_engine_cs *engine,
 	if (!to->legacy_hw_ctx.initialized)
 		return false;
 
-	if (to->ppgtt &&
-	    !(intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings))
+	if (ppgtt && (intel_engine_flag(engine) & ppgtt->pd_dirty_rings))
 		return false;
 
 	return to == engine->last_context;
 }
 
 static bool
-needs_pd_load_pre(struct intel_engine_cs *engine, struct intel_context *to)
+needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt,
+		  struct intel_engine_cs *engine,
+		  struct intel_context *to)
 {
-	if (!to->ppgtt)
+	if (!ppgtt)
 		return false;
 
+	/* Always load the ppgtt on first use */
+	if (!engine->last_context)
+		return true;
+
+	/* Same context without new entries, skip */
 	if (engine->last_context == to &&
-	    !(intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings))
+	    !(intel_engine_flag(engine) & ppgtt->pd_dirty_rings))
 		return false;
 
 	if (engine->id != RCS)
@@ -666,9 +652,11 @@ needs_pd_load_pre(struct intel_engine_cs *engine, struct intel_context *to)
 }
 
 static bool
-needs_pd_load_post(struct intel_context *to, u32 hw_flags)
+needs_pd_load_post(struct i915_hw_ppgtt *ppgtt,
+		   struct intel_context *to,
+		   u32 hw_flags)
 {
-	if (!to->ppgtt)
+	if (!ppgtt)
 		return false;
 
 	if (!IS_GEN8(to->i915))
@@ -684,11 +672,12 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 {
 	struct intel_context *to = req->ctx;
 	struct intel_engine_cs *engine = req->engine;
+	struct i915_hw_ppgtt *ppgtt = to->ppgtt ?: req->i915->mm.aliasing_ppgtt;
 	struct intel_context *from;
 	u32 hw_flags;
 	int ret, i;
 
-	if (skip_rcs_switch(engine, to))
+	if (skip_rcs_switch(ppgtt, engine, to))
 		return 0;
 
 	/* Trying to pin first makes error handling easier. */
@@ -719,13 +708,13 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	if (ret)
 		goto unpin_out;
 
-	if (needs_pd_load_pre(engine, to)) {
+	if (needs_pd_load_pre(ppgtt, engine, to)) {
 		/* Older GENs and non render rings still want the load first,
 		 * "PP_DCLV followed by PP_DIR_BASE register through Load
 		 * Register Immediate commands in Ring Buffer before submitting
 		 * a context."*/
 		trace_switch_mm(engine, to);
-		ret = to->ppgtt->switch_mm(to->ppgtt, req);
+		ret = ppgtt->switch_mm(ppgtt, req);
 		if (ret)
 			goto unpin_out;
 	}
@@ -736,16 +725,11 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 		 * space. This means we must enforce that a page table load
 		 * occur when this occurs. */
 		hw_flags = MI_RESTORE_INHIBIT;
-	else if (to->ppgtt &&
-		 intel_engine_flag(engine) & to->ppgtt->pd_dirty_rings)
+	else if (ppgtt && intel_engine_flag(engine) & ppgtt->pd_dirty_rings)
 		hw_flags = MI_FORCE_RESTORE;
 	else
 		hw_flags = 0;
 
-	/* We should never emit switch_mm more than once */
-	WARN_ON(needs_pd_load_pre(engine, to) &&
-		needs_pd_load_post(to, hw_flags));
-
 	if (to != from || (hw_flags & MI_FORCE_RESTORE)) {
 		ret = mi_set_context(req, hw_flags);
 		if (ret)
@@ -780,9 +764,9 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	/* GEN8 does *not* require an explicit reload if the PDPs have been
 	 * setup, and we do not wish to move them.
 	 */
-	if (needs_pd_load_post(to, hw_flags)) {
+	if (needs_pd_load_post(ppgtt, to, hw_flags)) {
 		trace_switch_mm(engine, to);
-		ret = to->ppgtt->switch_mm(to->ppgtt, req);
+		ret = ppgtt->switch_mm(ppgtt, req);
 		/* The hardware context switch is emitted, but we haven't
 		 * actually changed the state - so it's probably safe to bail
 		 * here. Still, let the user know something dangerous has
@@ -792,8 +776,8 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 			return ret;
 	}
 
-	if (to->ppgtt)
-		to->ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
+	if (ppgtt)
+		ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
 
 	for (i = 0; i < MAX_L3_SLICES; i++) {
 		if (!(to->remap_slice & (1<<i)))
@@ -846,17 +830,18 @@ int i915_switch_context(struct drm_i915_gem_request *req)
 	if (engine->id != RCS ||
 	    req->ctx->legacy_hw_ctx.rcs_state == NULL) {
 		struct intel_context *to = req->ctx;
+		struct i915_hw_ppgtt *ppgtt =
+			to->ppgtt ?: req->i915->mm.aliasing_ppgtt;
 
-		if (needs_pd_load_pre(engine, to)) {
+		if (needs_pd_load_pre(ppgtt, engine, to)) {
 			int ret;
 
 			trace_switch_mm(engine, to);
-			ret = to->ppgtt->switch_mm(to->ppgtt, req);
+			ret = ppgtt->switch_mm(ppgtt, req);
 			if (ret)
 				return ret;
 
-			/* Doing a PD load always reloads the page dirs */
-			to->ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
+			ppgtt->pd_dirty_rings &= ~intel_engine_flag(engine);
 		}
 
 		if (to != engine->last_context) {

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -2193,20 +2193,6 @@ int i915_ppgtt_init_hw(struct drm_device *dev)
 	return 0;
 }
 
-int i915_ppgtt_init_ring(struct drm_i915_gem_request *req)
-{
-	struct drm_i915_private *dev_priv = req->i915;
-	struct i915_hw_ppgtt *ppgtt = dev_priv->mm.aliasing_ppgtt;
-
-	if (i915.enable_execlists)
-		return 0;
-
-	if (!ppgtt)
-		return 0;
-
-	return ppgtt->switch_mm(ppgtt, req);
-}
-
 struct i915_hw_ppgtt *
 i915_ppgtt_create(struct drm_device *dev, struct drm_i915_file_private *fpriv)
 {

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -522,7 +522,6 @@ void i915_ggtt_cleanup_hw(struct drm_device *dev);
 
 int i915_ppgtt_init(struct drm_device *dev, struct i915_hw_ppgtt *ppgtt);
 int i915_ppgtt_init_hw(struct drm_device *dev);
-int i915_ppgtt_init_ring(struct drm_i915_gem_request *req);
 void i915_ppgtt_release(struct kref *kref);
 struct i915_hw_ppgtt *i915_ppgtt_create(struct drm_device *dev,
 					struct drm_i915_file_private *fpriv);