[Intel-gfx] [PATCH 1/6] drm/i915: mark the global default (intel_)context as such

[Dave Gordon]

Some of the LRC-specific context-destruction code has to special-case
the global default context, bacause the HWSP is part of that context. At
present it deduces it indirectly by checking for the backpointer from
the engine to the context, but that's an unsafe assumption if the setup
and teardown code is reorganised. (It could also test ctx->file_priv ==
NULL, but again that's a detail that might be subject to change).

So here we explicitly flag the default context at the point of creation,
and then reorganise the code in intel_lr_context_free() not to rely on
the ring->default_pointer (still) being set up; to iterate over engines
in reverse, as this is teardown code; and to reduce the nesting
level so it's easier to read.

Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         |  2 ++
 drivers/gpu/drm/i915/i915_gem_context.c | 12 +++++++-----
 drivers/gpu/drm/i915/intel_lrc.c        | 25 ++++++++++++-------------
 3 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9b82c45..666d07c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -854,6 +854,7 @@ struct i915_ctx_hang_stats {
  * @ref: reference count.
  * @user_handle: userspace tracking identity for this context.
  * @remap_slice: l3 row remapping information.
+ * @is_default: true iff this is the global default context
  * @flags: context specific flags:
  *         CONTEXT_NO_ZEROMAP: do not allow mapping things to page 0.
  * @file_priv: filp associated with this context (NULL for global default
@@ -872,6 +873,7 @@ struct intel_context {
 	struct kref ref;
 	int user_handle;
 	uint8_t remap_slice;
+	uint8_t is_global_default;
 	struct drm_i915_private *i915;
 	int flags;
 	struct drm_i915_file_private *file_priv;
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 900ffd0..5d3e287 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -241,8 +241,10 @@ __create_hw_context(struct drm_device *dev,
 				DEFAULT_CONTEXT_HANDLE, 0, GFP_KERNEL);
 		if (ret < 0)
 			goto err_out;
-	} else
+	} else {
+		ctx->is_global_default = true;
 		ret = DEFAULT_CONTEXT_HANDLE;
+	}
 
 	ctx->file_priv = file_priv;
 	ctx->user_handle = ret;
@@ -269,7 +271,6 @@ static struct intel_context *
 i915_gem_create_context(struct drm_device *dev,
 			struct drm_i915_file_private *file_priv)
 {
-	const bool is_global_default_ctx = file_priv == NULL;
 	struct intel_context *ctx;
 	int ret = 0;
 
@@ -279,8 +280,9 @@ i915_gem_create_context(struct drm_device *dev,
 	if (IS_ERR(ctx))
 		return ctx;
 
-	if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state) {
-		/* We may need to do things with the shrinker which
+	if (ctx->is_global_default && ctx->legacy_hw_ctx.rcs_state) {
+		/*
+		 * We may need to do things with the shrinker which
 		 * require us to immediately switch back to the default
 		 * context. This can cause a problem as pinning the
 		 * default context also requires GTT space which may not
@@ -313,7 +315,7 @@ i915_gem_create_context(struct drm_device *dev,
 	return ctx;
 
 err_unpin:
-	if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state)
+	if (ctx->is_global_default && ctx->legacy_hw_ctx.rcs_state)
 		i915_gem_object_ggtt_unpin(ctx->legacy_hw_ctx.rcs_state);
 err_destroy:
 	idr_remove(&file_priv->context_idr, ctx->user_handle);
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 3aa6147..23f90b2 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2367,22 +2367,21 @@ void intel_lr_context_free(struct intel_context *ctx)
 {
 	int i;
 
-	for (i = 0; i < I915_NUM_RINGS; i++) {
+	for (i = I915_NUM_RINGS; --i >= 0; ) {
+		struct intel_ringbuffer *ringbuf = ctx->engine[i].ringbuf;
 		struct drm_i915_gem_object *ctx_obj = ctx->engine[i].state;
 
-		if (ctx_obj) {
-			struct intel_ringbuffer *ringbuf =
-					ctx->engine[i].ringbuf;
-			struct intel_engine_cs *ring = ringbuf->ring;
+		if (!ctx_obj)
+			continue;
 
-			if (ctx == ring->default_context) {
-				intel_unpin_ringbuffer_obj(ringbuf);
-				i915_gem_object_ggtt_unpin(ctx_obj);
-			}
-			WARN_ON(ctx->engine[ring->id].pin_count);
-			intel_ringbuffer_free(ringbuf);
-			drm_gem_object_unreference(&ctx_obj->base);
+		if (ctx->is_global_default) {
+			intel_unpin_ringbuffer_obj(ringbuf);
+			i915_gem_object_ggtt_unpin(ctx_obj);
 		}
+
+		WARN_ON(ctx->engine[i].pin_count);
+		intel_ringbuffer_free(ringbuf);
+		drm_gem_object_unreference(&ctx_obj->base);
 	}
 }
 
@@ -2443,7 +2442,7 @@ static void lrc_setup_hardware_status_page(struct intel_engine_cs *ring,
  */
 
 int intel_lr_context_deferred_alloc(struct intel_context *ctx,
-				     struct intel_engine_cs *ring)
+				    struct intel_engine_cs *ring)
 {
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_gem_object *ctx_obj;
-- 
1.9.1