It is impossible to pass the PAT setting when sharing the fd. 1. All api , include vaapi, vulkan, gl... need such extension , the impact is huge. Even these API level accept , some middle ware , such as ffmpeg... also will reject it. 2. PAT is intel specific implementation , and MTL , LNL has different value and meanings, you could not expect application developer understand the details, it should be transparent to application developer. Thanks Carl
From: Yang, Fei <fei.y...@intel.com> Sent: Friday, June 9, 2023 11:13 PM To: Andi Shyti <andi.sh...@linux.intel.com>; Zhang, Carl <carl.zh...@intel.com> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>; Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>; Chris Wilson <ch...@chris-wilson.co.uk>; Roper, Matthew D <matthew.d.ro...@intel.com>; Justen, Jordan L <jordan.l.jus...@intel.com>; Gu, Lihao <lihao...@intel.com>; Intel GFX <intel-gfx@lists.freedesktop.org>; DRI Devel <dri-de...@lists.freedesktop.org> Subject: Re: [PATCH v17 1/1] drm/i915: Allow user to set cache at BO creation > Hi Carl, > >>>> besides this, ask a dumb question. >>>> How we retrieve the pat_index from a shared resource though dma_buf fd? >>>> maybe we need to know whether it could be CPU cached if we want map it. >>>> Of course, looks there are no real usage to access it though CPU. >>>> Just use it directly without any pat related options ? >>> >>> I am not understanding. Do you want to ask the PAT table to the driver? Are >>> you referring to the CPU PAT index? >>> >>> In any case, if I understood correctly, you don't necessarily always need to >>> set the PAT options and the cache options will fall into the default values. >>> >>> Please let me know if I haven't answered the question. >>> >> >> If mesa create a resource , then use DRM_IOCTL_PRIME_HANDLE_TO_FD convert it >> to a dma fd. >> Then share it to media, media use DRM_IOCTL_PRIME_FD_TO_HANDLE convert it to >> a gem bo. >> But media does not know the PAT index , because mesa create it and set it. >> So, if media want to call DRM_IOCTL_I915_GEM_MMAP_OFFSET, media does not >> know whether it could be WB. > > That's a good point. To be honest I am not really sure how this > is handled. > > Fei, Jordan? Do you have suggestion here? Is it possible to pass the PAT setting when sharing the fd? Or perhaps we should have kept the get_caching ioctl functional? Joonas, could you chime in here? > Andi
