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Date:   Thu, 27 Feb 2020 14:21:37 +0100
From:   Gerd Hoffmann <kraxel@redhat.com>
To:     Thomas =?utf-8?Q?Hellstr=C3=B6m_=28VMware=29?= 
        <thomas_os@shipmail.org>
Cc:     dri-devel@lists.freedesktop.org, Guillaume.Gardet@arm.com,
        David Airlie <airlied@linux.ie>,
        open list <linux-kernel@vger.kernel.org>,
        gurchetansingh@chromium.org, tzimmermann@suse.de, yuq825@gmail.com,
        noralf@tronnes.org, robh@kernel.org
Subject: Re: [PATCH v5 1/3] drm/shmem: add support for per object caching
 flags.
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  Hi,

> > So I'd like to push patches 1+2 to -fixes and sort everything else later
> > in -next.  OK?
> 
> OK with me.

Done.

>> [ context: why shmem helpers use pgprot_writecombine + pgprot_decrypted?
>>            we get conflicting mappings because of that, linear kernel
>>            map vs. gem object vmap/mmap ]

> Do we have any idea what drivers are actually using
> write-combine and decrypted?

drivers/gpu/drm# find -name Kconfig* -print | xargs grep -l DRM_GEM_SHMEM_HELPER
./lima/Kconfig
./tiny/Kconfig
./cirrus/Kconfig
./Kconfig
./panfrost/Kconfig
./udl/Kconfig
./v3d/Kconfig
./virtio/Kconfig

virtio needs cached.
cirrus+udl should be ok with cached too.

Not clue about the others (lima, tiny, panfrost, v3d).  Maybe they use
write-combine just because this is what they got by default from
drm_gem_mmap_obj().  Maybe they actually need that.  Trying to Cc:
maintainters (and drop stable@).

On decrypted: I guess that is only relevant for virtual machines, i.e.
virtio-gpu and cirrus?

virtio-gpu needs it, otherwise the host can't show the virtual display.
cirrus bounces everything via blits to vram, so it should be ok without
decrypted.  I guess that implies we should make decrypted configurable.

cheers,
  Gerd