Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT
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- To: Tomasz Figa <tfiga@xxxxxxxxxxxx>
- Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT
- From: Christoph Hellwig <hch@xxxxxx>
- Date: Wed, 19 Aug 2020 15:54:55 +0200
- Cc: Christoph Hellwig <hch@xxxxxx>, Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>, Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>, "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>, Joonyoung Shim <jy0922.shim@xxxxxxxxxxx>, Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>, Kyungmin Park <kyungmin.park@xxxxxxxxxxx>, Ben Skeggs <bskeggs@xxxxxxxxxx>, Pawel Osciak <pawel@xxxxxxxxxx>, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>, Matt Porter <mporter@xxxxxxxxxxxxxxxxxxx>, "list@xxxxxxx:IOMMU DRIVERS <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>," <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, alsa-devel@xxxxxxxxxxxxxxxx, linux-samsung-soc <linux-samsung-soc@xxxxxxxxxxxxxxx>, linux-ia64@xxxxxxxxxxxxxxx, linux-scsi@xxxxxxxxxxxxxxx, linux-parisc@xxxxxxxxxxxxxxx, Linux Doc Mailing List <linux-doc@xxxxxxxxxxxxxxx>, nouveau@xxxxxxxxxxxxxxxxxxxxx, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, linux-nvme@xxxxxxxxxxxxxxxxxxx, linux-mips@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, netdev@xxxxxxxxxxxxxxx, "list@xxxxxxx:IOMMU DRIVERS <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>," <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, Linux Media Mailing List <linux-media@xxxxxxxxxxxxxxx>
- In-reply-to: <CAAFQd5COLxjydDYrfx47ht8tj-aNPiaVnC+WyQA7nvpW4gs=ww@mail.gmail.com>
- References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <CAAFQd5COLxjydDYrfx47ht8tj-aNPiaVnC+WyQA7nvpW4gs=ww@mail.gmail.com>
- User-agent: Mutt/1.5.17 (2007-11-01)
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@xxxxxx> 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.
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