# Re: \[PATCH 05/28\] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2020-08-20 04:43:56 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/08/6074956
- Thread: https://ratatoskr.run/alsa-devel/2020/08/6073543/t.md

```text
On Wed, Aug 19, 2020 at 03:57:53PM +0200, Tomasz Figa wrote:
> > > Could you explain what makes you think it's unused? It's a feature of
> > > the UAPI generally supported by the videobuf2 framework and relied on
> > > by Chromium OS to get any kind of reasonable performance when
> > > accessing V4L2 buffers in the userspace.
> >
> > Because it doesn't do anything except on PARISC and non-coherent MIPS,
> > so by definition it isn't used by any of these media drivers.
> 
> It's still an UAPI feature, so we can't simply remove the flag, it
> must stay there as a no-op, until the problem is resolved.

Ok, I'll switch to just ignoring it for the next version.

> Also, it of course might be disputable as an out-of-tree usage, but
> selecting CONFIG_DMA_NONCOHERENT_CACHE_SYNC makes the flag actually do
> something on other platforms, including ARM64.

It isn't just disputable, but by kernel policies simply is not relevant.

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