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, 19 Dec 2018 06:51:22 -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 19, 2018 at 05:18:35PM +0900, Tomasz Figa wrote:
> The existing code that deals with dma_alloc_attrs() without
> DMA_ATTR_NON_CONSISTENT would just call dma_get_sgtable_attrs() like
> here:

I know.  And dma_get_sgtable_attrs is fundamentally flawed and we
need to kill this interface as it just can't worked with virtually
tagged cases.  It is a prime example for an interface that looks
nice and simple but is plain wrong.