drm/i915: Allow the application to choose the constant addressing mode

The relative-to-general state default is useless as it means having to
rewrite the streaming kernels for each batch. Relative-to-surface is
more useful, as that stream usually needs to be rewritten for each
batch. And absolute addressing mode, vital if you start streaming
state, is also only available by adjusting the register...
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_dma.c

@@ -778,6 +778,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
 	case I915_PARAM_HAS_COHERENT_RINGS:
 		value = 1;
 		break;
+	case I915_PARAM_HAS_EXEC_CONSTANTS:
+		value = INTEL_INFO(dev)->gen >= 4;
+		break;
 	default:
 		DRM_DEBUG_DRIVER("Unknown parameter %d\n",
 				 param->param);

drivers/gpu/drm/i915/i915_drv.h

@@ -258,6 +258,7 @@ typedef struct drm_i915_private {
 	const struct intel_device_info *info;
 
 	int has_gem;
+	int relative_constants_mode;
 
 	void __iomem *regs;
 

drivers/gpu/drm/i915/i915_gem.c

@@ -3735,6 +3735,8 @@ i915_gem_load(struct drm_device *dev)
 		}
 	}
 
+	dev_priv->relative_constants_mode = I915_EXEC_CONSTANTS_REL_GENERAL;
+
 	/* Old X drivers will take 0-2 for front, back, depth buffers */
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		dev_priv->fence_reg_start = 3;

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -957,7 +957,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	struct intel_ring_buffer *ring;
 	u32 exec_start, exec_len;
 	u32 seqno;
-	int ret, i;
+	int ret, mode, i;
 
 	if (!i915_gem_check_execbuffer(args)) {
 		DRM_ERROR("execbuf with invalid offset/length\n");
@@ -997,6 +997,39 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
+	mode = args->flags & I915_EXEC_CONSTANTS_MASK;
+	switch (mode) {
+	case I915_EXEC_CONSTANTS_REL_GENERAL:
+	case I915_EXEC_CONSTANTS_ABSOLUTE:
+	case I915_EXEC_CONSTANTS_REL_SURFACE:
+		if (ring == &dev_priv->ring[RCS] &&
+		    mode != dev_priv->relative_constants_mode) {
+			if (INTEL_INFO(dev)->gen < 4)
+				return -EINVAL;
+
+			if (INTEL_INFO(dev)->gen > 5 &&
+			    mode == I915_EXEC_CONSTANTS_REL_SURFACE)
+				return -EINVAL;
+
+			ret = intel_ring_begin(ring, 4);
+			if (ret)
+				return ret;
+
+			intel_ring_emit(ring, MI_NOOP);
+			intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));
+			intel_ring_emit(ring, INSTPM);
+			intel_ring_emit(ring,
+					I915_EXEC_CONSTANTS_MASK << 16 | mode);
+			intel_ring_advance(ring);
+
+			dev_priv->relative_constants_mode = mode;
+		}
+		break;
+	default:
+		DRM_ERROR("execbuf with unknown constants: %d\n", mode);
+		return -EINVAL;
+	}
+
 	if (args->buffer_count < 1) {
 		DRM_ERROR("execbuf with %d buffers\n", args->buffer_count);
 		return -EINVAL;

include/drm/i915_drm.h

@@ -289,6 +289,7 @@ typedef struct drm_i915_irq_wait {
 #define I915_PARAM_HAS_BLT		 11
 #define I915_PARAM_HAS_RELAXED_FENCING	 12
 #define I915_PARAM_HAS_COHERENT_RINGS	 13
+#define I915_PARAM_HAS_EXEC_CONSTANTS	 14
 
 typedef struct drm_i915_getparam {
 	int param;
@@ -635,6 +636,17 @@ struct drm_i915_gem_execbuffer2 {
 #define I915_EXEC_RENDER                 (1<<0)
 #define I915_EXEC_BSD                    (2<<0)
 #define I915_EXEC_BLT                    (3<<0)
+
+/* Used for switching the constants addressing mode on gen4+ RENDER ring.
+ * Gen6+ only supports relative addressing to dynamic state (default) and
+ * absolute addressing.
+ *
+ * These flags are ignored for the BSD and BLT rings.
+ */
+#define I915_EXEC_CONSTANTS_MASK 	(3<<6)
+#define I915_EXEC_CONSTANTS_REL_GENERAL (0<<6) /* default */
+#define I915_EXEC_CONSTANTS_ABSOLUTE 	(1<<6)
+#define I915_EXEC_CONSTANTS_REL_SURFACE (2<<6) /* gen4/5 only */
 	__u64 flags;
 	__u64 rsvd1;
 	__u64 rsvd2;