linux-kernel - Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations

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Message-ID: <20210617100656.GA11107@lst.de>
Date:   Thu, 17 Jun 2021 12:06:56 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Christoph Hellwig <hch@....de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations

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.