linux-kernel - Re: [PATCH 1/2] of: Fix DMA mask generation

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Date:   Fri, 11 Aug 2017 19:56:41 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     robh+dt@...nel.org, frowand.list@...il.com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hch@....de, m.szyprowski@...sung.com,
        stefan.wahren@...e.com, afaerber@...e.de, hverkuil@...all.nl,
        johan@...nel.org
Subject: Re: [PATCH 1/2] of: Fix DMA mask generation

On Fri, Aug 11, 2017 at 05:29:56PM +0100, Robin Murphy wrote:
> Historically, DMA masks have suffered some ambiguity between whether
> they represent the range of physical memory a device can access, or the
> address bits a device is capable of driving, particularly since on many
> platforms the two are equivalent. Whilst there are some stragglers left
> (dma_max_pfn(), I'm looking at you...), the majority of DMA code has
> been cleaned up to follow the latter definition, not least since it is
> the only one which makes sense once IOMMUs are involved.

I think it always was supposed to be the latter, but that doesn't mean
that everyone got the message :)

> Either of these patches alone should be sufficient to un-break RPi3,
> and they apply independently, so I'm quite happy for one to go in as a
> fix now and the other to wait for 4.14.

This one is something I'm comfortable feeding to Linus for 4.13
if I get a few ACKs from people familar with the OF code and intended
meaning of the ranges in the device tree.