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

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Message-ID: <20200901110617.GA13232@lst.de>
Date:   Tue, 1 Sep 2020 13:06:17 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Christoph Hellwig <hch@....de>, 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 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?

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.