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Date:   Thu, 20 Aug 2020 07:20:04 +0200
From:   Christoph Hellwig <>
To:     Tomasz Figa <>
        Linux Doc Mailing List <>,,,,
        "James E.J. Bottomley" <>,, Christoph Hellwig <>,
        linux-samsung-soc <>,
        Joonyoung Shim <>,,
        Kyungmin Park <>,
        Ben Skeggs <>,
        Matt Porter <>,
        Linux Media Mailing List <>,
        Tom Lendacky <>,
        Pawel Osciak <>,
        Mauro Carvalho Chehab <>,
        " DRIVERS <>, Joerg
        Roedel <>, " <>,
        Thomas Bogendoerfer <>,,,
        Seung-Woo Kim <>,
        Linux Kernel Mailing List <>,
        " DRIVERS <>, Joerg
        Roedel <>, " <>
Subject: Re: [PATCH 05/28] media/v4l2: remove

On Thu, Aug 20, 2020 at 06:43:47AM +0200, Christoph Hellwig wrote:
> 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.

So I took a deeper look.  I don't really think it qualifies as a UAPI
in our traditional sense.  For one it only appeared in 5.9-rc1, so we
can trivially expedite the patch into 5.9-rc and not actually make it
show up in any released kernel version.  And even as of the current
Linus' tree the only user is a test driver.  So I really think the best
way to go ahead is to just revert it ASAP as the design wasn't thought
out at all.

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