linux-kernel - Re: [PATCH v5 2/2] media: usb: pwc: Don't use coherent DMA buffers for ISO transfer

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Date:   Wed, 12 Dec 2018 01:09:17 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        "Matwey V. Kornilov" <matwey@....msu.ru>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Matwey V. Kornilov" <matwey.kornilov@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Ezequiel Garcia <ezequiel@...labora.com>, hdegoede@...hat.com,
        Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        rostedt@...dmis.org, mingo@...hat.com,
        Mike Isely <isely@...ox.com>,
        Bhumika Goyal <bhumirks@...il.com>,
        Colin King <colin.king@...onical.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        keiichiw@...omium.org
Subject: Re: [PATCH v5 2/2] media: usb: pwc: Don't use coherent DMA buffers
 for ISO transfer

On Wed, Dec 12, 2018 at 05:57:02PM +0900, Tomasz Figa wrote:
> How about dma_sync_sg_*()? I'd expect some drivers to export/import
> such memory via sg, since that's the typical way of describing memory
> in DMA-buf.

The way it is implemented dma_sync_sg_* would just work, however there
really should be no need to have sglists for buffers created by this
API.

> Sounds good to me. Thanks for working on this. I'd be happy to be on
> CC and help with review when you post the patches later.

The patches were already posted here:

https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031982.html