[Intel-gfx] [PATCH] drm/i915: Extract context switch skip and add pd load logic

[Michel Thierry]

From: Ben Widawsky <benjamin.widawsky at intel.com>

This patch just breaks out the logic of context switch skip.

It also adds pd load pre, and pd load post logic (for GEN8).

v2: Use new functions to replace the logic right away (Daniel)
v3: Add missing pd load logic.

Cc: Daniel Vetter <daniel at ffwll.ch>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
Signed-off-by: Michel Thierry <michel.thierry at intel.com> (v2+)
---
 drivers/gpu/drm/i915/i915_gem_context.c | 48 +++++++++++++++++++++++++++++++--
 1 file changed, 46 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 70346b0..8474e2c 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -569,6 +569,33 @@ mi_set_context(struct intel_engine_cs *ring,
 	return ret;
 }
 
+static inline bool should_skip_switch(struct intel_engine_cs *ring,
+				      struct intel_context *from,
+				      struct intel_context *to)
+{
+	if (from == to && !to->remap_slice)
+		return true;
+
+	return false;
+}
+
+static bool
+needs_pd_load_pre(struct intel_engine_cs *ring, struct intel_context *to)
+{
+	struct drm_i915_private *dev_priv = ring->dev->dev_private;
+
+	return ((INTEL_INFO(ring->dev)->gen < 8) ||
+			(ring != &dev_priv->ring[RCS])) && to->ppgtt;
+}
+
+static bool
+needs_pd_load_post(struct intel_engine_cs *ring, struct intel_context *to)
+{
+	return (!to->legacy_hw_ctx.initialized ||
+			i915_gem_context_is_default(to)) &&
+			to->ppgtt && IS_GEN8(ring->dev);
+}
+
 static int do_switch(struct intel_engine_cs *ring,
 		     struct intel_context *to)
 {
@@ -584,7 +611,7 @@ static int do_switch(struct intel_engine_cs *ring,
 		BUG_ON(!i915_gem_obj_is_pinned(from->legacy_hw_ctx.rcs_state));
 	}
 
-	if (from == to && !to->remap_slice)
+	if (should_skip_switch(ring, from, to))
 		return 0;
 
 	/* Trying to pin first makes error handling easier. */
@@ -602,7 +629,11 @@ static int do_switch(struct intel_engine_cs *ring,
 	 */
 	from = ring->last_context;
 
-	if (to->ppgtt) {
+	if (needs_pd_load_pre(ring, 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(ring, to);
 		ret = to->ppgtt->switch_mm(to->ppgtt, ring);
 		if (ret)
@@ -644,6 +675,19 @@ static int do_switch(struct intel_engine_cs *ring,
 	if (ret)
 		goto unpin_out;
 
+	if (needs_pd_load_post(ring, to)) {
+		ret = to->ppgtt->switch_mm(to->ppgtt, ring);
+		/* 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
+		 * happened.
+		 */
+		if (ret) {
+			DRM_ERROR("Failed to change address space on context switch\n");
+			goto unpin_out;
+		}
+	}
+
 	for (i = 0; i < MAX_L3_SLICES; i++) {
 		if (!(to->remap_slice & (1<<i)))
 			continue;
-- 
2.1.1