Hi Fei, > 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> Andi
