On Tue, Dec 17, 2019 at 03:02:28PM -0800, Gurchetan Singh wrote:
> I'm just going to put Chia's review comment here since it sums
> the issue rather nicely:
>
> "(1) Semantically, a dma-buf is in DMA domain. CPU access from the
> importer must be surrounded by {begin,end}_cpu_access. This gives the
> exporter a chance to move the buffer to the CPU domain temporarily.
>
> (2) When the exporter itself has other means to do CPU access, it is
> only reasonable for the exporter to move the buffer to the CPU domain
> before access, and to the DMA domain after access. The exporter can
> potentially reuse {begin,end}_cpu_access for that purpose.
>
> Because of (1), udmabuf does need to implement the
> {begin,end}_cpu_access hooks. But "begin" should mean
> dma_sync_sg_for_cpu and "end" should mean dma_sync_sg_for_device.
>
> Because of (2), if userspace wants to continuing accessing through the
> memfd mapping, it should call udmabuf's {begin,end}_cpu_access to
> avoid cache issues."
>
> Reported-by: Chia-I Wu <olva...@gmail.com>
> Suggested-by: Chia-I Wu <olva...@gmail.com>
> Fixes: 284562e1f348 ("udmabuf: implement begin_cpu_access/end_cpu_access
> hooks")
> Signed-off-by: Gurchetan Singh <gurchetansi...@chromium.org>
Pushed to drm-misc-next.
thanks,
Gerd
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
