From: Qiang Yu <yuq825@gmail.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "Thomas Hellström (VMware)" <thomas_os@shipmail.org>,
dri-devel <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,
noralf@tronnes.org, "Rob Herring" <robh@kernel.org>
Subject: Re: [PATCH v5 1/3] drm/shmem: add support for per object caching flags.
Date: Mon, 2 Mar 2020 09:56:52 +0800 [thread overview]
Message-ID: <CAKGbVbspOgJmKpuuNYTew-3LoT_Pr0rRNJVjzkd83c=UXTki1Q@mail.gmail.com> (raw)
In-Reply-To: <20200227132137.irruicvlkxpdo3so@sirius.home.kraxel.org>
On Thu, Feb 27, 2020 at 9:21 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>
> 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@).
>
lima driver needs writecombine mapped buffer for GPU hardware
working properly due to CPU-GPU not cache coherent. Although we
haven't meet problems caused by kernel/user map conflict, but I
do admit it's a problem as I met with amdgpu+arm before.
With TTM we can control page allocated and create a pool for
writecombine pages, but seems shmem is not friendly with
writecombine pages.
Thanks,
Qiang
next prev parent reply other threads:[~2020-03-02 1:57 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200226154752.24328-1-kraxel@redhat.com>
2020-02-26 15:47 ` [PATCH v5 1/3] drm/shmem: add support for per object caching flags Gerd Hoffmann
2020-02-26 16:51 ` Guillaume Gardet
2020-02-26 18:24 ` Thomas Hellström (VMware)
2020-02-27 0:02 ` Chia-I Wu
2020-02-27 7:16 ` Thomas Hellström (VMware)
2020-02-27 7:53 ` Gerd Hoffmann
2020-02-27 8:10 ` Thomas Hellström (VMware)
2020-02-27 10:56 ` Gerd Hoffmann
2020-02-27 12:16 ` Thomas Hellström (VMware)
2020-02-27 13:21 ` Gerd Hoffmann
2020-02-27 13:44 ` Thomas Hellström (VMware)
2020-02-27 13:49 ` Thomas Hellström (VMware)
2020-02-28 9:49 ` Gerd Hoffmann
2020-02-28 9:54 ` Thomas Hellström (VMware)
2020-02-28 10:46 ` Gerd Hoffmann
2020-03-02 1:56 ` Qiang Yu [this message]
2020-02-26 15:47 ` [PATCH v5 2/3] drm/virtio: fix mmap page attributes Gerd Hoffmann
2020-02-26 16:52 ` Guillaume Gardet
2020-02-26 15:47 ` [PATCH v5 3/3] drm/udl: simplify gem object mapping Gerd Hoffmann
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