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

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Message-ID: <CAAFQd5BDh05DNPShr54opY2GyY-FcH7g8=V2t4xBwz0OwRu9xQ@mail.gmail.com>
Date:   Tue, 8 Sep 2020 23:58:22 +0200
From:   Tomasz Figa <tfiga@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Christoph Hellwig <hch@....de>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT

Hi Hans, Mauro,

On Tue, Sep 1, 2020 at 5:02 PM Tomasz Figa <tfiga@...omium.org> wrote:
>
> 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.

Given the above, we would like to make changes that affect the UAPI.
Would you still be able to revert this series?

Best regards,
Tomasz