[PATCH] drm/i915/gtt: add some flushing for the 64K GTT path

[Matthew Auld]

If we need to mark the PDE as operating in 64K GTT mode, we should be
paranoid and flush the extra writes, like we already do for the PTEs. On
some platforms the clflush can apparently add the just the right amount
of magical delay to force the GPU to see the updated entry.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
index 6e0e52eeb87a..6a5af995f5b1 100644
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -548,6 +548,7 @@ static void gen8_ppgtt_insert_huge(struct i915_vma *vma,
 					      I915_GTT_PAGE_SIZE_2M)))) {
 			vaddr = px_vaddr(pd);
 			vaddr[maybe_64K] |= GEN8_PDE_IPS_64K;
+			clflush_cache_range(vaddr, PAGE_SIZE);
 			page_size = I915_GTT_PAGE_SIZE_64K;
 
 			/*
@@ -568,6 +569,7 @@ static void gen8_ppgtt_insert_huge(struct i915_vma *vma,
 				for (i = 1; i < index; i += 16)
 					memset64(vaddr + i, encode, 15);
 
+				clflush_cache_range(vaddr, PAGE_SIZE);
 			}
 		}
 
-- 
2.26.3