[Intel-xe] [PATCH v6 0/5] PAT and cache coherency support

[Souza, Jose]

On Thu, 2023-09-28 at 12:40 -0700, José Roberto de Souza wrote:
> On Thu, 2023-09-28 at 11:05 +0100, Matthew Auld wrote:
> > Branch available here:
> > https://gitlab.freedesktop.org/mwa/kernel/-/tree/xe-pat-index?ref_type=heads
> > 
> > Goal here is to allow userspace to directly control the pat_index when mapping
> > memory via the ppGTT, in addtion to the CPU caching mode. This is very much
> > needed on newer igpu platforms which allow incoherent GT access, where the
> > choice over the cache level and expected coherency is best left to userspace
> > depending on their usecase.  In the future there may also be other stuff encoded
> > in the pat_index, so giving userspace direct control will also be needed there.
> > 
> > To support this we added new gem_create uAPI for selecting the CPU cache
> > mode to use for system memory, including the expected GPU coherency mode. There
> > are various restrictions here for the selected coherency mode and compatible CPU
> > cache modes.  With that in place the actual pat_index can now be provided as
> > part of vm_bind. The only restriction is that the coherency mode of the
> > pat_index must be at least as coherent as the gem_create coherency mode. There
> > are also some special cases like with userptr and dma-buf.
> > 
> > v2:
> >   - Loads of improvements/tweaks. Main changes are to now allow
> >     gem_create.coh_mode <= coh_mode(pat_index), rather than it needing to match
> >     exactly. This simplifies the dma-buf policy from userspace pov. Also we now
> >     only consider COH_NONE and COH_AT_LEAST_1WAY.
> > v3:
> >   - Rebase. Split the pte_encode() refactoring, plus various smaller tweaks and
> >     fixes.
> > v4:
> >   - Rebase on Lucas' new series.
> >   - Drop UC cache mode.
> >   - s/smem_cpu_caching/cpu_caching/. Idea is to make VRAM WC explicit in the
> >     uapi, plus make it more future proof.
> > v5:
> >   - Rebase, plus some small tweaks and fixes.
> > v6:
> >   - CI hooks fixes + checkpatch.
> > 
> 
> With comment in patch 3/6 fixed this series is:
> Reviewed-by: José Roberto de Souza <jose.souza at intel.com>
> Tested-by: José Roberto de Souza <jose.souza at intel.com>

Here the Mesa implementation: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25462

> 
> Thank you