On 04/05/2023 00:02, fei.yang@xxxxxxxxx wrote:
From: Fei Yang <fei.yang@xxxxxxxxx>
Currently the KMD is using enum i915_cache_level to set caching policy for
buffer objects. This is flaky because the PAT index which really controls
the caching behavior in PTE has far more levels than what's defined in the
enum. In addition, the PAT index is platform dependent, having to translate
between i915_cache_level and PAT index is not reliable, and makes the code
more complicated.
From UMD's perspective there is also a necessity to set caching policy for
performance fine tuning. It's much easier for the UMD to directly use PAT
index because the behavior of each PAT index is clearly defined in Bspec.
Having the abstracted i915_cache_level sitting in between would only cause
more ambiguity.
For these reasons this patch replaces i915_cache_level with PAT index. Also
note, the cache_level is not completely removed yet, because the KMD still
has the need of creating buffer objects with simple cache settings such as
cached, uncached, or writethrough. For such simple cases, using cache_level
would help simplify the code.
Cc: Chris Wilson <chris.p.wilson@xxxxxxxxxxxxxxx>
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
Signed-off-by: Fei Yang <fei.yang@xxxxxxxxx>
Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
[snip]
diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
index bb6998d67133..f2334a713c4e 100644
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
+++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
@@ -56,7 +56,7 @@ static u64 gen8_pte_encode(dma_addr_t addr,
}
^^^
How come there are no changes to gen8_pte_encode?
vvv
static u64 mtl_pte_encode(dma_addr_t addr,
- enum i915_cache_level level,
+ unsigned int pat_index,
u32 flags)
Prototype and implementation changed here for mtl_pte_encode.
And we have:
if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
ppgtt->vm.pte_encode = mtl_pte_encode;
else
ppgtt->vm.pte_encode = gen8_pte_encode;
So should be same prototype. And:
u64 (*pte_encode)(dma_addr_t addr,
- enum i915_cache_level level,
+ unsigned int pat_index,
u32 flags); /* Create a valid PTE */
Patch relies on the compiler considering enum equal to unsigned int?
But the implementation of gen8_pte_encode and most ggtt counterparts is
looking at the passed in pat index and thinks it is cache level.
How is that supposed to work?! Or I am blind and am missing something?
Regards,
Tvrtko
