drm/i915: Emit to ringbuffer directly

This removes the usage of intel_ring_emit in favour of
directly writing to the ring buffer.

intel_ring_emit was preventing the compiler for optimising
fetch and increment of the current ring buffer pointer and
therefore generating very verbose code for every write.

It had no useful purpose since all ringbuffer operations
are started and ended with intel_ring_begin and
intel_ring_advance respectively, with no bail out in the
middle possible, so it is fine to increment the tail in
intel_ring_begin and let the code manage the pointer
itself.

Useless instruction removal amounts to approximately
two and half kilobytes of saved text on my build.

Not sure if this has any measurable performance
implications but executing a ton of useless instructions
on fast paths cannot be good.

v2:
 * Change return from intel_ring_begin to error pointer by
   popular demand.
 * Move tail increment to intel_ring_advance to enable some
   error checking.

v3:
 * Move tail advance back into intel_ring_begin.
 * Rebase and tidy.

v4:
 * Complete rebase after a few months since v3.

v5:
 * Remove unecessary cast and fix !debug compile. (Chris Wilson)

v6:
 * Make intel_ring_offset take request as well.
 * Fix recording of request postfix plus a sprinkle of asserts.
   (Chris Wilson)

v7:
 * Use intel_ring_offset to get the postfix. (Chris Wilson)
 * Convert GVT code as well.

v8:
 * Rename *out++ to *cs++.

v9:
 * Fix GVT out to cs conversion in GVT.

v10:
 * Rebase for new intel_ring_begin in selftests.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170214113242.29241-1-tvrtko.ursulin@linux.intel.com

1 files changed, 34 insertions, 45 deletions

diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
index 0608fad7f593..5ef9f5bfb92c 100644
--- a/drivers/gpu/drm/i915/intel_overlay.c
+++ b/drivers/gpu/drm/i915/intel_overlay.c
@@ -267,8 +267,7 @@ static int intel_overlay_on(struct intel_overlay *overlay)
 {
 	struct drm_i915_private *dev_priv = overlay->i915;
 	struct drm_i915_gem_request *req;
-	struct intel_ring *ring;
-	int ret;
+	u32 *cs;
 
 	WARN_ON(overlay->active);
 	WARN_ON(IS_I830(dev_priv) && !(dev_priv->quirks & QUIRK_PIPEA_FORCE));
@@ -277,10 +276,10 @@ static int intel_overlay_on(struct intel_overlay *overlay)
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	ret = intel_ring_begin(req, 4);
-	if (ret) {
+	cs = intel_ring_begin(req, 4);
+	if (IS_ERR(cs)) {
 		i915_add_request_no_flush(req);
-		return ret;
+		return PTR_ERR(cs);
 	}
 
 	overlay->active = true;
@@ -288,12 +287,11 @@ static int intel_overlay_on(struct intel_overlay *overlay)
 	if (IS_I830(dev_priv))
 		i830_overlay_clock_gating(dev_priv, false);
 
-	ring = req->ring;
-	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_ON);
-	intel_ring_emit(ring, overlay->flip_addr | OFC_UPDATE);
-	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
-	intel_ring_emit(ring, MI_NOOP);
-	intel_ring_advance(ring);
+	*cs++ = MI_OVERLAY_FLIP | MI_OVERLAY_ON;
+	*cs++ = overlay->flip_addr | OFC_UPDATE;
+	*cs++ = MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP;
+	*cs++ = MI_NOOP;
+	intel_ring_advance(req, cs);
 
 	return intel_overlay_do_wait_request(overlay, req, NULL);
 }
@@ -326,10 +324,8 @@ static int intel_overlay_continue(struct intel_overlay *overlay,
 {
 	struct drm_i915_private *dev_priv = overlay->i915;
 	struct drm_i915_gem_request *req;
-	struct intel_ring *ring;
 	u32 flip_addr = overlay->flip_addr;
-	u32 tmp;
-	int ret;
+	u32 tmp, *cs;
 
 	WARN_ON(!overlay->active);
 
@@ -345,16 +341,15 @@ static int intel_overlay_continue(struct intel_overlay *overlay,
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	ret = intel_ring_begin(req, 2);
-	if (ret) {
+	cs = intel_ring_begin(req, 2);
+	if (IS_ERR(cs)) {
 		i915_add_request_no_flush(req);
-		return ret;
+		return PTR_ERR(cs);
 	}
 
-	ring = req->ring;
-	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE);
-	intel_ring_emit(ring, flip_addr);
-	intel_ring_advance(ring);
+	*cs++ = MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE;
+	*cs++ = flip_addr;
+	intel_ring_advance(req, cs);
 
 	intel_overlay_flip_prepare(overlay, vma);
 
@@ -408,9 +403,7 @@ static void intel_overlay_off_tail(struct i915_gem_active *active,
 static int intel_overlay_off(struct intel_overlay *overlay)
 {
 	struct drm_i915_gem_request *req;
-	struct intel_ring *ring;
-	u32 flip_addr = overlay->flip_addr;
-	int ret;
+	u32 *cs, flip_addr = overlay->flip_addr;
 
 	WARN_ON(!overlay->active);
 
@@ -424,25 +417,23 @@ static int intel_overlay_off(struct intel_overlay *overlay)
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	ret = intel_ring_begin(req, 6);
-	if (ret) {
+	cs = intel_ring_begin(req, 6);
+	if (IS_ERR(cs)) {
 		i915_add_request_no_flush(req);
-		return ret;
+		return PTR_ERR(cs);
 	}
 
-	ring = req->ring;
-
 	/* wait for overlay to go idle */
-	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE);
-	intel_ring_emit(ring, flip_addr);
-	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
+	*cs++ = MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE;
+	*cs++ = flip_addr;
+	*cs++ = MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP;
 
 	/* turn overlay off */
-	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_OFF);
-	intel_ring_emit(ring, flip_addr);
-	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
+	*cs++ = MI_OVERLAY_FLIP | MI_OVERLAY_OFF;
+	*cs++ = flip_addr;
+	*cs++ = MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP;
 
-	intel_ring_advance(ring);
+	intel_ring_advance(req, cs);
 
 	intel_overlay_flip_prepare(overlay, NULL);
 
@@ -465,6 +456,7 @@ static int intel_overlay_recover_from_interrupt(struct intel_overlay *overlay)
 static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
 {
 	struct drm_i915_private *dev_priv = overlay->i915;
+	u32 *cs;
 	int ret;
 
 	lockdep_assert_held(&dev_priv->drm.struct_mutex);
@@ -478,23 +470,20 @@ static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
 	if (I915_READ(ISR) & I915_OVERLAY_PLANE_FLIP_PENDING_INTERRUPT) {
 		/* synchronous slowpath */
 		struct drm_i915_gem_request *req;
-		struct intel_ring *ring;
 
 		req = alloc_request(overlay);
 		if (IS_ERR(req))
 			return PTR_ERR(req);
 
-		ret = intel_ring_begin(req, 2);
-		if (ret) {
+		cs = intel_ring_begin(req, 2);
+		if (IS_ERR(cs)) {
 			i915_add_request_no_flush(req);
-			return ret;
+			return PTR_ERR(cs);
 		}
 
-		ring = req->ring;
-		intel_ring_emit(ring,
-				MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
-		intel_ring_emit(ring, MI_NOOP);
-		intel_ring_advance(ring);
+		*cs++ = MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP;
+		*cs++ = MI_NOOP;
+		intel_ring_advance(req, cs);
 
 		ret = intel_overlay_do_wait_request(overlay, req,
 						    intel_overlay_release_old_vid_tail);