[Intel-gfx] [PATCH 04/13] drm/i915: Compute the ELSP register location once

[Chris Wilson]

Similar to the issue with reading from the context status buffer, we
frequently write to the ELSP register (4 writes per interrupt) and know
we hold the required spinlock and forcewake throughout. We can
shortcircuit the I915_WRITE() by precomputing the address of the ELSP
register and avoid all the known checks.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 25e0972e7166..15873e69e7fe 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -331,10 +331,11 @@ uint64_t intel_lr_context_descriptor(struct i915_gem_context *ctx,
 static void execlists_elsp_write(struct drm_i915_gem_request *rq0,
 				 struct drm_i915_gem_request *rq1)
 {
-
 	struct intel_engine_cs *engine = rq0->engine;
 	struct drm_i915_private *dev_priv = rq0->i915;
-	uint64_t desc[2];
+	u32 __iomem *elsp =
+		dev_priv->regs + i915_mmio_reg_offset(RING_ELSP(engine));
+	u64 desc[2];
 
 	if (rq1) {
 		desc[1] = intel_lr_context_descriptor(rq1->ctx, rq1->engine);
@@ -347,15 +348,12 @@ static void execlists_elsp_write(struct drm_i915_gem_request *rq0,
 	rq0->elsp_submitted++;
 
 	/* You must always write both descriptors in the order below. */
-	I915_WRITE_FW(RING_ELSP(engine), upper_32_bits(desc[1]));
-	I915_WRITE_FW(RING_ELSP(engine), lower_32_bits(desc[1]));
+	writel(upper_32_bits(desc[1]), elsp);
+	writel(lower_32_bits(desc[1]), elsp);
 
-	I915_WRITE_FW(RING_ELSP(engine), upper_32_bits(desc[0]));
+	writel(upper_32_bits(desc[0]), elsp);
 	/* The context is automatically loaded after the following */
-	I915_WRITE_FW(RING_ELSP(engine), lower_32_bits(desc[0]));
-
-	/* ELSP is a wo register, use another nearby reg for posting */
-	POSTING_READ_FW(RING_EXECLIST_STATUS_LO(engine));
+	writel(lower_32_bits(desc[0]), elsp);
 }
 
 static void
-- 
2.9.3