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