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

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Message-ID: <56425BBF.6000308@codeaurora.org>
Date:	Tue, 10 Nov 2015 15:03:59 -0600
From:	Timur Tabi <timur@...eaurora.org>
To:	Arnd Bergmann <arnd@...db.de>
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 11/10/2015 01:13 PM, Arnd Bergmann wrote:
> If the mask is 64-bit by default on ARM64, that is a bug that we need
> to fix urgently. Can you verify this?

I think the mask is 0 by default, because there's no code in ARM64 that 
actually sets the mask.

Take a look at arch_setup_pdev_archdata() in 
arch/powerpc/kernel/setup-common.c.

void arch_setup_pdev_archdata(struct platform_device *pdev)
{
         pdev->archdata.dma_mask = DMA_BIT_MASK(32);
         pdev->dev.dma_mask = &pdev->archdata.dma_mask;
         set_dma_ops(&pdev->dev, &dma_direct_ops);
}

I don't see anything equivalent in arch/arm64

> A lot of PCI devices can only do 32-bit DMA, and we have plenty
> of drivers that don't bother setting a mask at all because the 32-bit
> mask is the default on all other architectures.

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.

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Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the
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