lkml.org 
[lkml]   [2020]   [Aug]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT
On Wed, Aug 19, 2020 at 3:55 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Wed, Aug 19, 2020 at 01:16:51PM +0200, Tomasz Figa wrote:
> > Hi Christoph,
> >
> > On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch@lst.de> wrote:
> > >
> > > The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused,
> >
> > 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.

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.

Best regards,
Tomasz

\
 
 \ /
  Last update: 2022-09-17 16:08    [W:0.263 / U:0.828 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site