Re: [PATCH v17 1/1] drm/i915: Allow user to set cache at BO creation

[Andi Shyti <andi.shyti@linux.intel.com>]

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?

Andi