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

[Zhao Yakui]

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 writting 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.

Signed-off-by: Zhao Yakui <yakui.zhao at intel.com>
CC: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 10deebe..a76ea83 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;
@@ -2738,7 +2740,7 @@ 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);
@@ -2756,7 +2758,7 @@ 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;
-- 
2.7.4