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Date:   Wed, 7 Oct 2020 14:24:18 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tomasz Figa <tfiga@chromium.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
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Subject: Re: [PATCH 8/8] WIP: add a dma_alloc_contiguous API
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On Wed, Oct 07, 2020 at 02:21:43PM +0200, Tomasz Figa wrote:
> My initial feeling is that it should work, but we'll give you a
> definitive answer once we prototype it. :)
> 
> We might actually give it a try in the USB HCD subsystem as well, to
> implement usb_alloc_noncoherent(), as an optimization for drivers
> which have to perform multiple random accesses to the URB buffers. I
> think you might recall discussing this by the way of the pwc and
> uvcvideo camera drivers.

Yes.  I guess for usb the dma_alloc_noncoherent as-is in linux-next
might be better.   So if you have the cycles please prototype it
either way, although for that we'd also need at least a
mmap_noncoherent method, and probaby a get_sgtable_noncoherent one.