From d53028334db3066e64b88f1d4a0f587150612d8f Mon Sep 17 00:00:00 2001
From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Date: Mon, 11 May 2020 19:08:03 +0300
Subject: drm/i915/gt: Force pte cacheline to main memory
Git-commit: 84eac0c65940d9633247b0c8c826d4bcb7307351
Patch-mainline: v5.8-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

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.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1840
Testcase: igt/gem_exec_fence/parallel
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200511160803.15407-1-mika.kuoppala@linux.intel.com
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 15 +++++++++++++--
 1 file changed, 13 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..2dc88e76ebec 100644
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -389,6 +389,16 @@ static int gen8_ppgtt_alloc(struct i915_address_space *vm,
 	return err;
 }
 
+static __always_inline inline void
+write_pte(gen8_pte_t *pte, const gen8_pte_t val)
+{
+	/* Magic delays? Or can we refine these to flush all in one pass? */
+	*pte = val;
+	wmb(); /* cpu to cache */
+	clflush(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 +415,8 @@ 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 +498,7 @@ 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;
-- 
2.28.0