[PATCH 4/5 v2] drm/i915: flush system agent TLBs on SNB

[Ben Widawsky <ben@bwidawsk.net>]

This allows us to map the PTEs WC. I've not done thorough testing or
performance measurements with this patch, but it should be decent.

This is based on a patch from Jesse with the original commit message
> I've only lightly tested this so far, but the corruption seems to be
> gone if I write the GFX_FLSH_CNTL reg after binding an object.  This
> register should control the TLB for the system agent, which is what CPU
> mapped objects will go through.

It has been updated for the new AGP-less code by me, and included with
it is feedback from the original patch.

v2: Updated to reflect paranoia on pte updates/register posting reads.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by [v1]: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 11 +++++++++--
 drivers/gpu/drm/i915/i915_reg.h     |  2 ++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 4abde31..9a5b035 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -379,6 +379,13 @@ static void gen6_ggtt_bind_object(struct drm_i915_gem_object *obj,
 	 */
 	if (i != 0)
 		WARN_ON(readl(&gtt_entries[i-1]) != pte_encode(dev, addr, level));
+
+	/* This next bit makes the above posting read even more important. We
+	 * want to flush the TLBs only after we're certain all the PTE updates
+	 * have finished.
+	 */
+	I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
+	POSTING_READ(GFX_FLSH_CNTL_GEN6);
 }
 
 void i915_gem_gtt_bind_object(struct drm_i915_gem_object *obj,
@@ -589,8 +596,8 @@ int i915_gem_gtt_init(struct drm_device *dev)
 		goto err_out;
 	}
 
-	dev_priv->mm.gtt->gtt = ioremap(gtt_bus_addr,
-					dev_priv->mm.gtt->gtt_total_entries * sizeof(gtt_pte_t));
+	dev_priv->mm.gtt->gtt = ioremap_wc(gtt_bus_addr,
+					   dev_priv->mm.gtt->gtt_total_entries * sizeof(gtt_pte_t));
 	if (!dev_priv->mm.gtt->gtt) {
 		DRM_ERROR("Failed to map the gtt page table\n");
 		teardown_scratch_page(dev);
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 9de463f..7942838 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -688,6 +688,8 @@
 #define   CM0_RC_OP_FLUSH_DISABLE (1<<0)
 #define BB_ADDR		0x02140 /* 8 bytes */
 #define GFX_FLSH_CNTL	0x02170 /* 915+ only */
+#define GFX_FLSH_CNTL_GEN6	0x101008
+#define   GFX_FLSH_CNTL_EN	(1<<0)
 #define ECOSKPD		0x021d0
 #define   ECO_GATING_CX_ONLY	(1<<3)
 #define   ECO_FLIP_DONE		(1<<0)
-- 
1.8.0