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

From: Arnd Bergmann
Date: Tue Nov 10 2015 - 17:09:49 EST

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.

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