[Intel-xe] [PATCH v2 0/6] PAT and cache coherency support

[Souza, Jose]

On Thu, 2023-09-14 at 16:31 +0100, Matthew Auld wrote:
> Branch available here (lightly tested):
> https://gitlab.freedesktop.org/mwa/kernel/-/tree/xe-pat-index?ref_type=heads
> 
> Series still needs some more testing. Also note that the series directly depends
> on the WIP patch here: https://patchwork.freedesktop.org/series/122708/
> 
> 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 for system memory. 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.
> 


Getting constant DMAR errors after loading Xe KMD on TGL with your branch in framebuffer console, logs attached.


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