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From:   Tomasz Figa <tfiga@chromium.org>
Date:   Fri, 18 Jun 2021 12:21:33 +0900
Message-ID: <CAAFQd5CgLDkJ3t1aU2PRcGu6cGFjLXOnvMqDg62Z7Zuc8ABVHg@mail.gmail.com>
Subject: Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations
To:     Christoph Hellwig <hch@lst.de>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Ricardo Ribalda <ribalda@chromium.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Jun 17, 2021 at 7:07 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Thu, Jun 17, 2021 at 06:40:58PM +0900, Tomasz Figa wrote:
> > Sorry, I meant dma_alloc_attrs() and yes, it's indeed a misnomer. Our
> > use case basically has no need for the additional coherent mapping, so
> > creation of it can be skipped to save some vmalloc space. (Yes, it
> > probably only matters for 32-bit architectures.)
>
> Yes, that is the normal use case, and it is solved by using
> dma_alloc_noncoherent or dma_alloc_noncontigous without the vmap
> step.

True, silly me. Probably not enough coffee at the time I was looking at it.

With that, wouldn't it be possible to completely get rid of
dma_alloc_{coherent,attrs}() and use dma_alloc_noncontiguous() +
optional kernel and/or userspace mapping helper everywhere? (Possibly
renaming it to something as simple as dma_alloc().