[Intel-gfx] [PATCH 187/190] drm/i915: Allow execbuffer to use the first object as the batch

[Chris Wilson]

Currently, the last object in the execlist is the always the batch.
However, when building the batch buffer we often know the batch object
first and if we can use the first slot in the execlist we can emit
relocation instructions relative to it immediately and avoid a separate
pass to adjust the relocations to point to the last execlist slot.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c            | 3 +++
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 5 ++++-
 include/uapi/drm/i915_drm.h                | 4 +++-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index c1afbd873197..85926c03c3cf 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -172,6 +172,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
 	case I915_PARAM_HAS_EXEC_SOFTPIN:
 		value = 1;
 		break;
+	case I915_PARAM_HAS_EXEC_BATCH_FIRST:
+		value = 1;
+		break;
 	default:
 		DRM_DEBUG("Unknown parameter %d\n", param->param);
 		return -EINVAL;
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index eac3d52f790d..817c0cc054d2 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -415,7 +415,10 @@ ht_head(const struct intel_context *ctx, u32 handle)
 
 static int eb_batch_index(const struct i915_execbuffer *eb)
 {
-	return eb->args->buffer_count - 1;
+	 if (eb->args->flags & I915_EXEC_BATCH_FIRST)
+		 return 0;
+	 else
+		 return eb->args->buffer_count - 1;
 }
 
 static int
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index ff7b438059da..27bb4668af05 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -357,6 +357,7 @@ typedef struct drm_i915_irq_wait {
 #define I915_PARAM_HAS_GPU_RESET	 35
 #define I915_PARAM_HAS_RESOURCE_STREAMER 36
 #define I915_PARAM_HAS_EXEC_SOFTPIN	 37
+#define I915_PARAM_HAS_EXEC_BATCH_FIRST	 38
 
 typedef struct drm_i915_getparam {
 	__s32 param;
@@ -786,7 +787,8 @@ struct drm_i915_gem_execbuffer2 {
  */
 #define I915_EXEC_RESOURCE_STREAMER     (1<<15)
 
-#define __I915_EXEC_UNKNOWN_FLAGS -(I915_EXEC_RESOURCE_STREAMER<<1)
+#define I915_EXEC_BATCH_FIRST		(1<<16)
+#define __I915_EXEC_UNKNOWN_FLAGS (-(I915_EXEC_BATCH_FIRST<<1))
 
 #define I915_EXEC_CONTEXT_ID_MASK	(0xffffffff)
 #define i915_execbuffer2_set_context_id(eb2, context) \
-- 
2.7.0.rc3