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From:   Tomasz Figa <tfiga@chromium.org>
Date:   Wed, 7 Oct 2020 14:21:43 +0200
Message-ID: <CAAFQd5AtN-ykAF_2mAqGxVugeEegYxfYdS6gD4O3zCY1jznNYA@mail.gmail.com>
Subject: Re: [PATCH 8/8] WIP: add a dma_alloc_contiguous API
To:     Christoph Hellwig <hch@lst.de>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        "open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>
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On Wed, Oct 7, 2020 at 8:21 AM Christoph Hellwig <hch@lst.de> wrote:
>
> On Tue, Oct 06, 2020 at 10:56:04PM +0200, Tomasz Figa wrote:
> > > Yes.  And make sure the API isn't implemented when VIVT caches are
> > > used, but that isn't really different from the current interface.
> >
> > Okay, thanks. Let's see if we can make necessary changes to the videobuf2.
> >
> > +Sergey Senozhatsky for awareness too.
>
> I can defer the changes a bit to see if you'd really much prefer
> the former interface.  I think for now the most important thing is
> that it works properly for the potential users, and the prime one is
> videobuf2 for now.  drm also seems like a big potential users, but I
> had a really hard time getting the developers to engage in API
> development.

My initial feeling is that it should work, but we'll give you a
definitive answer once we prototype it. :)

We might actually give it a try in the USB HCD subsystem as well, to
implement usb_alloc_noncoherent(), as an optimization for drivers
which have to perform multiple random accesses to the URB buffers. I
think you might recall discussing this by the way of the pwc and
uvcvideo camera drivers.

Best regards,
Tomasz