[PATCH V2] drm/i915: Use I915_MAP_WC for execlists context buffer on the platforms without LLC

* [PATCH V2] drm/i915: Use I915_MAP_WC for execlists context buffer on the platforms without LLC
@ 2018-06-22  6:09 Zhao Yakui
  2018-06-22  6:26 ` Chris Wilson
                   ` (2 more replies)
  0 siblings, 3 replies; 9+ messages in thread
From: Zhao Yakui @ 2018-06-22  6:09 UTC (permalink / raw)
  To: intel-gfx

Under execlists mode the context buffer is allocated in global Gtt region.
The I915_MAP_WB type is used to map the buffer so that the driver can
initialize the context buffer.(Ring reg, Context Ctrl reg and so on).
And then __context_pin is called to flush back corresponding contents.
In fact as it also tries to update context buffer (Ring Tail offset)
before writing the ELSP port, it has no explicit cache flsuh.Maybe it is
handled by HW. But this is quite confusing as BXT has no LLC. So the WC
is used to map the context buffer on the platform without LLC and the
update of context buffer is writen into phys page directly. It will
be safer.

V1->V2: Remove the dirty flag of execlists state buffer and one minor
typo in commit log

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
CC: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 10deebe..5ffd76e 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1386,6 +1386,7 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 {
 	void *vaddr;
 	int ret;
+	enum i915_map_type map = HAS_LLC(ctx->i915) ? I915_MAP_WB : I915_MAP_WC;
 
 	ret = execlists_context_deferred_alloc(ctx, engine, ce);
 	if (ret)
@@ -1396,7 +1397,7 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 	if (ret)
 		goto err;
 
-	vaddr = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
+	vaddr = i915_gem_object_pin_map(ce->state->obj, map);
 	if (IS_ERR(vaddr)) {
 		ret = PTR_ERR(vaddr);
 		goto unpin_vma;
@@ -2728,6 +2729,7 @@ populate_lr_context(struct i915_gem_context *ctx,
 		    struct intel_engine_cs *engine,
 		    struct intel_ring *ring)
 {
+	enum i915_map_type map = HAS_LLC(ctx->i915) ? I915_MAP_WB : I915_MAP_WC;
 	void *vaddr;
 	u32 *regs;
 	int ret;
@@ -2738,13 +2740,12 @@ populate_lr_context(struct i915_gem_context *ctx,
 		return ret;
 	}
 
-	vaddr = i915_gem_object_pin_map(ctx_obj, I915_MAP_WB);
+	vaddr = i915_gem_object_pin_map(ctx_obj, map);
 	if (IS_ERR(vaddr)) {
 		ret = PTR_ERR(vaddr);
 		DRM_DEBUG_DRIVER("Could not map object pages! (%d)\n", ret);
 		return ret;
 	}
-	ctx_obj->mm.dirty = true;
 
 	if (engine->default_state) {
 		/*
@@ -2756,7 +2757,7 @@ populate_lr_context(struct i915_gem_context *ctx,
 		void *defaults;
 
 		defaults = i915_gem_object_pin_map(engine->default_state,
-						   I915_MAP_WB);
+						   map);
 		if (IS_ERR(defaults)) {
 			ret = PTR_ERR(defaults);
 			goto err_unpin_ctx;
@@ -2851,6 +2852,7 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
 	struct intel_engine_cs *engine;
 	struct i915_gem_context *ctx;
 	enum intel_engine_id id;
+	enum i915_map_type map = HAS_LLC(dev_priv) ? I915_MAP_WB : I915_MAP_WC;
 
 	/* Because we emit WA_TAIL_DWORDS there may be a disparity
 	 * between our bookkeeping in ce->ring->head and ce->ring->tail and
@@ -2872,7 +2874,7 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
 				continue;
 
 			reg = i915_gem_object_pin_map(ce->state->obj,
-						      I915_MAP_WB);
+						      map);
 			if (WARN_ON(IS_ERR(reg)))
 				continue;
 
@@ -2880,7 +2882,6 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
 			reg[CTX_RING_HEAD+1] = 0;
 			reg[CTX_RING_TAIL+1] = 0;
 
-			ce->state->obj->mm.dirty = true;
 			i915_gem_object_unpin_map(ce->state->obj);
 
 			intel_ring_reset(ce->ring, 0);
-- 
2.7.4

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