[Intel-gfx] [PATCH] drm/i915: Force pte cacheline to main memory

[Mika Kuoppala]

We have problems of tgl not seeing a valid pte entry
when iommu is enabled. Add heavy handed flushing
of entry modification by flushing the cpu, cacheline
and then wcb. This forces the pte out to main memory
past this point regarless of promises of coherency.

This is an evolution of an experimental patch from
Chris Wilson of adding wmb for coherent partners,
by adding a clflush to force the cache->memory step.

Testcase: igt/gem_exec_fence/parallel
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
index 94e746af8926..6b13408b0e38 100644
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -389,6 +389,15 @@ static int gen8_ppgtt_alloc(struct i915_address_space *vm,
 	return err;
 }
 
+static __always_inline inline void
+write_pte(gen8_pte_t * const pte, const gen8_pte_t val)
+{
+	*pte = val;
+	wmb(); /* cpu to cache */
+	clflush((void *)pte); /* cache to memory */
+	wmb(); /* visible to all */
+}
+
 static __always_inline u64
 gen8_ppgtt_insert_pte(struct i915_ppgtt *ppgtt,
 		      struct i915_page_directory *pdp,
@@ -405,7 +414,8 @@ gen8_ppgtt_insert_pte(struct i915_ppgtt *ppgtt,
 	vaddr = kmap_atomic_px(i915_pt_entry(pd, gen8_pd_index(idx, 1)));
 	do {
 		GEM_BUG_ON(iter->sg->length < I915_GTT_PAGE_SIZE);
-		vaddr[gen8_pd_index(idx, 0)] = pte_encode | iter->dma;
+		write_pte(&vaddr[gen8_pd_index(idx, 0)],
+			  pte_encode | iter->dma);
 
 		iter->dma += I915_GTT_PAGE_SIZE;
 		if (iter->dma >= iter->max) {
@@ -487,7 +497,7 @@ static void gen8_ppgtt_insert_huge(struct i915_vma *vma,
 
 		do {
 			GEM_BUG_ON(iter->sg->length < page_size);
-			vaddr[index++] = encode | iter->dma;
+			write_pte(&vaddr[index++], encode | iter->dma);
 
 			start += page_size;
 			iter->dma += page_size;
-- 
2.17.1