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From: Arnd Bergmann <arnd@arndb.de>
To: Timur Tabi <timur@codeaurora.org>
Cc: Sinan Kaya <okaya@codeaurora.org>, dmaengine@vger.kernel.org,
        cov@codeaurora.org, jcm@redhat.com, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, Vinod Koul <vinod.koul@intel.com>,
        Dan Williams <dan.j.williams@intel.com>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] dma: add Qualcomm Technologies HIDMA channel driver
Date: Fri, 30 Oct 2015 23:47:46 +0100
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On Friday 30 October 2015 16:55:16 Timur Tabi wrote:
> 
> On 10/30/2015 04:42 PM, Sinan Kaya wrote:
> >>
> >>     if (WARN_ON(!pdev->dev.dma_mask))
> >>         return -ENXIO;
> >>
> >> The dma mask has to always be set by the platform code before probe()
> >> is called. If it is not set, you are not allowed to perform DMA.
> >
> > I tested this on an ACPI platform BTW when I was working on the initial
> > implementation.
> 
> PowerPC sets the mask to 32 bits by default:
> 
> http://lxr.free-electrons.com/ident?i=arch_setup_pdev_archdata
> 
> Should we do something similar in ARM64?  Today, we have to manually set 
> the DMA mask in all drivers.

We set the dma mask from the 'dma-ranges' property of the parent device,
but fall back to 32-bit because we did not manage to mandate this property
in time for all arm64 machines to use.

	Arnd