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

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Message-ID: <20210617085233.GA4702@lst.de>
Date:   Thu, 17 Jun 2021 10:52:33 +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@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 8/8] videobuf2: handle non-contiguous DMA allocations

On Thu, Jun 17, 2021 at 05:30:11PM +0900, Tomasz Figa wrote:
> We still have use cases for dma_alloc_coherent() and DMA_ATTR_NO_KERNEL_MAPPING.

dma_alloc_coherent does not take a flags argument, so you can't use
DMA_ATTR_NO_KERNEL_MAPPING with it.  What would your use case be here
anyway?  In general DMA_ATTR_NO_KERNEL_MAPPING is rather misnamed, as
usually there is a kernel mapping, just not one that is coherent and
should be used.