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

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Message-ID: <CAAFQd5CmPVSxmZJVn7HnNUn8srZbAbnfzpNMYw3KcDzn7xD2cg@mail.gmail.com>
Date:   Tue, 1 Sep 2020 17:02:20 +0200
From:   Tomasz Figa <tfiga@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     alsa-devel@...a-project.org, linux-ia64@...r.kernel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        nouveau@...ts.freedesktop.org, linux-nvme@...ts.infradead.org,
        linux-mips@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        linux-mm@...ck.org,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        linux-scsi@...r.kernel.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Matt Porter <mporter@...nel.crashing.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Pawel Osciak <pawel@...iak.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <linux-arm-kernel@...ts.infradead.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-parisc@...r.kernel.org, netdev@...r.kernel.org,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT

On Tue, Sep 1, 2020 at 1:06 PM Christoph Hellwig <hch@....de> wrote:
>
> On Thu, Aug 20, 2020 at 07:33:48PM +0200, Tomasz Figa wrote:
> > > It wasn't meant to be too insulting, but I found this out when trying
> > > to figure out how to just disable it.  But it also ends up using
> > > the actual dma attr flags for it's own consistency checks, so just
> > > not setting the flag did not turn out to work that easily.
> > >
> >
> > Yes, sadly the videobuf2 ended up becoming quite counterintuitive
> > after growing for the long years and that is reflected in the design
> > of this feature as well. I think we need to do something about it.
>
> So I'm about to respin the series and wonder how we should proceed.
> I've failed to come up with a clean patch to keep the flag and make
> it a no-op.  Can you or your team give it a spin?
>

Okay, I'll take a look.

> Also I wonder if the flag should be renamed from NON_CONSISTENT
> to NON_COHERENT - the consistent thing is a weird wart from the times
> the old PCI DMA API that is mostly gone now.

It originated from the DMA_ATTR_NON_CONSISTENT flag, but agreed that
NON_COHERENT would be more consistent (pun not intended) with the rest
of the DMA API given the removal of that flag. Let me see if we can
still change it.

Best regards,
Tomasz