linux-kernel - Re: [PATCH 2/2] dma: add Qualcomm Technologies HIDMA channel driver

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Message-ID: <5126606.XdciyP3Dft@wuerfel>
Date:	Fri, 30 Oct 2015 23:47:46 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Sinan Kaya <okaya@...eaurora.org>, dmaengine@...r.kernel.org,
	cov@...eaurora.org, jcm@...hat.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dma: add Qualcomm Technologies HIDMA channel driver

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
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