linux-kernel - Re: [RFC 2/3] USB: core: Add non-coherent buffer allocation helpers

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Date:   Thu, 30 Aug 2018 22:50:47 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     Christoph Hellwig <hch@...radead.org>, linux-media@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tomasz Figa <tfiga@...omium.org>,
        "Matwey V . Kornilov" <matwey@....msu.ru>,
        Alan Stern <stern@...land.harvard.edu>, kernel@...labora.com,
        Keiichi Watanabe <keiichiw@...omium.org>
Subject: Re: [RFC 2/3] USB: core: Add non-coherent buffer allocation helpers

On Thu, Aug 30, 2018 at 07:11:35PM -0300, Ezequiel Garcia wrote:
> On Thu, 2018-08-30 at 10:58 -0700, Christoph Hellwig wrote:
> > Please don't introduce new DMA_ATTR_NON_CONSISTENT users, it is
> > a rather horrible interface, and I plan to kill it off rather sooner
> > than later.  I plan to post some patches for a better interface
> > that can reuse the normal dma_sync_single_* interfaces for ownership
> > transfers.  I can happily include usb in that initial patch set based
> > on your work here if that helps.
> 
> Please do. Until we have proper allocators that go thru the DMA API,
> drivers will have to kmalloc the USB transfer buffers, and have
> streaming mappings. Which in turns mean not using IOMMU or CMA.

dma_map_page will of course use the iommu.