From: Eric Anholt <eric@anholt.net>
To: Rob Herring <robh+dt@kernel.org>, Tomeu Vizoso <tomeu@tomeuvizoso.net>
Cc: Boris Brezillon <boris.brezillon@collabora.com>,
dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/gem_shmem: Use a writecombine mapping for ->vaddr
Date: Fri, 31 May 2019 08:46:58 -0700 [thread overview]
Message-ID: <87woi6wrrh.fsf@anholt.net> (raw)
In-Reply-To: <20190529065121.13485-1-boris.brezillon@collabora.com>
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Boris Brezillon <boris.brezillon@collabora.com> writes:
> Right now, the BO is mapped as a cached region when ->vmap() is called
> and the underlying object is not a dmabuf.
> Doing that makes cache management a bit more complicated (you'd need
> to call dma_map/unmap_sg() on the ->sgt field everytime the BO is about
> to be passed to the GPU/CPU), so let's map the BO with writecombine
> attributes instead (as done in most drivers).
>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
> Found this issue while working on panfrost perfcnt where the GPU dumps
> perf counter values in memory and the CPU reads them back in
> kernel-space. This patch seems to solve the unpredictable behavior I
> had.
>
> I can also go for the other option (call dma_map/unmap/_sg() when
> needed) if you think that's more appropriate.
writecombined was the intent, and this makes kernel vmap match the
userspace mmap path.
Reviewed-by: Eric Anholt <eric@anholt.net>
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next prev parent reply other threads:[~2019-05-31 15:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-29 6:51 [PATCH] drm/gem_shmem: Use a writecombine mapping for ->vaddr Boris Brezillon
2019-05-29 6:58 ` Daniel Vetter
2019-05-31 15:46 ` Eric Anholt [this message]
2019-06-03 7:21 ` Daniel Vetter
2019-06-03 15:43 ` Eric Anholt
2019-06-03 15:57 ` Daniel Vetter
2019-06-10 15:40 ` Rob Herring
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