[Intel-gfx] [PATCH] drm/i915: Export a function to flush the context upon pinning

[Chris Wilson]

For legacy contexts we employ an optimisation to only flush the context
when binding into the global GTT. This avoids stalling onthe GPU when
reloading an active context. Wrap this detail up into a helper and
export it for a potential third user. (Longer term, context pinning
needs to be reworked as the current handling of switch context pins too
late and so risks eviction and corrupting the request. Plans, plans, plans.)

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h         |  3 +++
 drivers/gpu/drm/i915/i915_gem_context.c | 36 +++++++++++++++++++++++----------
 drivers/gpu/drm/i915/intel_ringbuffer.c | 11 +++++-----
 3 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b79845911676..5267f72b5b91 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3502,6 +3502,9 @@ int i915_gem_context_open(struct drm_device *dev, struct drm_file *file);
 void i915_gem_context_close(struct drm_device *dev, struct drm_file *file);
 int i915_switch_context(struct drm_i915_gem_request *req);
 int i915_gem_switch_to_kernel_context(struct drm_i915_private *dev_priv);
+struct i915_vma *
+i915_gem_context_pin_legacy(struct i915_gem_context *ctx,
+			    unsigned int flags);
 void i915_gem_context_free(struct kref *ctx_ref);
 struct drm_i915_gem_object *
 i915_gem_alloc_context_obj(struct drm_device *dev, size_t size);
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index d3e51d92e80a..dd226339470f 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -765,12 +765,33 @@ needs_pd_load_post(struct i915_hw_ppgtt *ppgtt,
 	return false;
 }
 
+struct i915_vma *
+i915_gem_context_pin_legacy(struct i915_gem_context *ctx,
+			    unsigned int flags)
+{
+	struct i915_vma *vma = ctx->engine[RCS].state;
+	int ret;
+
+	/* Clear this page out of any CPU caches for coherent swap-in/out. */
+	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
+		ret = i915_gem_object_set_to_gtt_domain(vma->obj, false);
+		if (ret)
+			return ERR_PTR(ret);
+	}
+
+	ret = i915_vma_pin(vma, 0, ctx->ggtt_alignment, PIN_GLOBAL | flags);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return vma;
+}
+
 static int do_rcs_switch(struct drm_i915_gem_request *req)
 {
 	struct i915_gem_context *to = req->ctx;
 	struct intel_engine_cs *engine = req->engine;
 	struct i915_hw_ppgtt *ppgtt = to->ppgtt ?: req->i915->mm.aliasing_ppgtt;
-	struct i915_vma *vma = to->engine[RCS].state;
+	struct i915_vma *vma;
 	struct i915_gem_context *from;
 	u32 hw_flags;
 	int ret, i;
@@ -778,17 +799,10 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	if (skip_rcs_switch(ppgtt, engine, to))
 		return 0;
 
-	/* Clear this page out of any CPU caches for coherent swap-in/out. */
-	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
-		ret = i915_gem_object_set_to_gtt_domain(vma->obj, false);
-		if (ret)
-			return ret;
-	}
-
 	/* Trying to pin first makes error handling easier. */
-	ret = i915_vma_pin(vma, 0, to->ggtt_alignment, PIN_GLOBAL);
-	if (ret)
-		return ret;
+	vma = i915_gem_context_pin_legacy(to, 0);
+	if (IS_ERR(vma))
+		return PTR_ERR(vma);
 
 	/*
 	 * Pin can switch back to the default context if we end up calling into
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d450d5a5326c..f91ee24e2763 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1951,14 +1951,13 @@ static int intel_ring_context_pin(struct i915_gem_context *ctx,
 		return 0;
 
 	if (ce->state) {
-		ret = i915_gem_object_set_to_gtt_domain(ce->state->obj, false);
-		if (ret)
-			goto error;
+		struct i915_vma *vma;
 
-		ret = i915_vma_pin(ce->state, 0, ctx->ggtt_alignment,
-				   PIN_GLOBAL | PIN_HIGH);
-		if (ret)
+		vma = i915_gem_context_pin_legacy(ctx, PIN_HIGH);
+		if (IS_ERR(vma)) {
+			ret = PTR_ERR(vma);
 			goto error;
+		}
 	}
 
 	/* The kernel context is only used as a placeholder for flushing the
-- 
2.10.1