linux-kernel - Re: [PATCH V2 1/3] scsi: mptxsas: try 64 bit DMA when 32 bit DMA fails

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Date:	Tue, 10 Nov 2015 23:08:57 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Sinan Kaya <okaya@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	linux-scsi@...r.kernel.org, jcm@...hat.com,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	linux-kernel@...r.kernel.org,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	cov@...eaurora.org, linux-arm-msm@...r.kernel.org,
	agross@...eaurora.org, MPT-FusionLinux.pdl@...gotech.com,
	Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH V2 1/3] scsi: mptxsas: try 64 bit DMA when 32 bit DMA fails

On Tuesday 10 November 2015 15:59:18 Timur Tabi wrote:
> On 11/10/2015 03:54 PM, Arnd Bergmann wrote:
> 
> >> In our drivers for 32-bit devices, we have to explicitly set the DMA
> >> mask to 32-bits in order to get any DMA working.
> >
> > Do you mean PCI devices or platform devices?
> 
> Platform.
> 
> > Maybe the parent bus is lacking a dma-ranges property?
> 
> All of this applies only on device-tree platforms.  Sinan and I are 
> working on an ACPI server platform.  So we never call 
> of_dma_configure(), and we don't have a dma-ranges property.

ACPI must have something else to mark DMA master devices and their
capabilities, right?

The platform should initialize the dma_mask pointer to a per-device
mask and set both the dma_mask and dma_coherent_mask to 32 bits
for any DMA master device, and the device driver should override
that to be an appropriate mask based on its needs later.

	Arnd
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