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Date:   Thu, 17 Jun 2021 12:06:56 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tomasz Figa <tfiga@chromium.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        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>
Subject: Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations
Message-ID: <20210617100656.GA11107@lst.de>
References: <20210427131344.139443-1-senozhatsky@chromium.org> <20210427131344.139443-9-senozhatsky@chromium.org> <10a0903a-e295-5cba-683a-1eb89a0804ed@xs4all.nl> <YMsAIVs7G2hUDR2F@google.com> <20210617080107.GA1422@lst.de> <CAAFQd5DiPstn-s+yQM3iMd=G9oaag39qCyX483a7-Jrn=gxWCA@mail.gmail.com> <20210617085233.GA4702@lst.de> <CAAFQd5DqK2gSTGjfo-vahXwMzzO9gv26cY=vV6urn3viDLPE7g@mail.gmail.com>
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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.