linux-kernel - Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc

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Message-ID: <20201130083150.GC32234@lst.de>
Date:   Mon, 30 Nov 2020 09:31:50 +0100
From:   Christoph Hellwig <hch@....de>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Ricardo Ribalda <ribalda@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        IOMMU DRIVERS <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Sergey Senozhatsky <senozhatsky@...gle.com>
Subject: Re: [PATCH v3 5/6] media: uvcvideo: Use dma_alloc_noncontiguos API

On Thu, Nov 26, 2020 at 08:44:50PM +0900, Sergey Senozhatsky wrote:
> > +	uvc_urb->buffer = vmap(uvc_urb->pages,
> > +			       PAGE_ALIGN(stream->urb_size) >> PAGE_SHIFT,
> > +			       VM_DMA_COHERENT, PAGE_KERNEL);
> 
> This is not related to Ricardo's patch, just a side note:
> 
>   I think VM_DMA_COHERENT needs to be renamed. I found it a bit confusing
>   to see DMA_COHERENT mapping being dma_sync-ed. It turned out that the
>   flag has different meaning.

s/renamed/removed/.  This is a normal VM_MAP mapping as far as the
core vmalloc/vmap code is concerned.  VM_DMA_COHERENT is only for
internal use in the core DMA code.