From: Gerd Hoffmann <kraxel@redhat.com>
To: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>,
Emil Velikov <emil.l.velikov@gmail.com>,
Sean Paul <sean@poorly.run>,
dri-devel <dri-devel@lists.freedesktop.org>,
Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH 1/2] drm/shmem: Use cached mappings by default
Date: Mon, 18 May 2020 12:11:32 +0200 [thread overview]
Message-ID: <20200518101132.ves2qswskaiajh2y@sirius.home.kraxel.org> (raw)
In-Reply-To: <3bc1a032-2e7a-d7a8-e5e6-8d53a9e9bd3a@suse.de>
On Mon, May 18, 2020 at 10:50:15AM +0200, Thomas Zimmermann wrote:
> Hi Gerd
>
> Am 18.05.20 um 10:23 schrieb Gerd Hoffmann:
> >>> $ git grep drm_gem_shmem_mmap
> >>>
> >>> We also need correct access from userspace, otherwise the gpu is going to
> >>> be sad.
> >>
> >> I've been thinking about this, and I think it means that we can never
> >> have cached mappings anywhere. Even if shmem supports it internally for
> >> most drivers, as soon as the page are exported, the importer could
> >> expect uncached memory.
> >
> > The importer should not expect anything but call dma-buf ops so the
> > exporter has a chance to handle this correctly.
>
> I have the following case in mind: Suppose the exporter maps cached
> pages and the importer expects uncached pages for DMA. There is
> map_dma_buf/unmap_dma_buf, which can implement a cache flush for the
> cached pages. Is it guaranteed that the importer calls this around each
> DMA operation?
I think the importer is supposed to do that, but I wouldn't surprised if
there are cases in tree where this isn't implemented correctly ...
take care,
Gerd
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next prev parent reply other threads:[~2020-05-18 10:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 15:03 [PATCH 0/2] Default to cachable mappings for GEM SHMEM Thomas Zimmermann
2020-05-13 15:03 ` [PATCH 1/2] drm/shmem: Use cached mappings by default Thomas Zimmermann
2020-05-13 15:06 ` Thomas Zimmermann
2020-05-14 12:40 ` Daniel Vetter
2020-05-14 15:27 ` Thomas Zimmermann
2020-05-14 20:36 ` Rob Herring
2020-05-15 6:58 ` Thomas Zimmermann
2020-05-15 14:10 ` Daniel Vetter
2020-05-18 8:13 ` Thomas Zimmermann
2020-05-18 8:23 ` Gerd Hoffmann
2020-05-18 8:50 ` Thomas Zimmermann
2020-05-18 10:11 ` Gerd Hoffmann [this message]
2020-05-18 14:40 ` Daniel Vetter
2020-05-19 6:31 ` Thomas Zimmermann
2020-05-13 15:03 ` [PATCH 2/2] drm/udl: Use GEM vmap/mmap function from SHMEM helpers Thomas Zimmermann
2020-05-13 15:49 ` Daniel Vetter
2020-05-13 17:19 ` Thomas Zimmermann
2020-05-14 12:44 ` Daniel Vetter
2020-05-19 6:36 ` Thomas Zimmermann
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