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

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Message-ID: <4fc5107f93871599ead017af7ad50f22535a7683.camel@collabora.com>
Date:   Thu, 30 Aug 2018 19:11:35 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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, 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.

Regards,
Eze