Re: [PATCH v8 2/2] drm/gem: Don't map imported GEMs

[Christian König]

Am 16.08.22 um 13:44 schrieb Dmitry Osipenko:
> [SNIP]
> > The other complication I noticed is that we don't seem to keep around
> > the fd after importing to a GEM handle.  And I could imagine that
> > doing so could cause issues with too many fd's.  So I guess the best
> > thing is to keep the status quo and let drivers that cannot mmap
> > imported buffers just fail mmap?
> That actually should be all the drivers excluding those that use
> DRM-SHMEM because only DRM-SHMEM uses dma_buf_mmap(), that's why it
> works for Panfrost. I'm pretty sure mmaping of imported GEMs doesn't
> work for the MSM driver, isn't it?
>
> Intel and AMD drivers don't allow to map the imported dma-bufs. Both
> refuse to do the mapping.
>
> Although, AMDGPU "succeeds" to do the mapping using
> AMDGPU_GEM_DOMAIN_GTT, but then touching the mapping causes bus fault,
> hence mapping actually fails. I think it might be the AMDGPU
> driver/libdrm bug, haven't checked yet.

That's then certainly broken somehow. Amdgpu should nerve ever have 
allowed to mmap() imported DMA-bufs and the last time I check it didn't.

Regards,
Christian.

> So we're back to the point that neither of DRM drivers need to map
> imported dma-bufs and this was never tested. In this case this patch is
> valid, IMO.