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Date:	Mon, 22 Dec 2014 23:44:52 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Murali Karicheri <m-karicheri2@...com>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, grant.likely@...aro.org,
	robh+dt@...nel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, will.deacon@....com
Subject: Re: [RFC v1 PATCH 1/2] of/pci: add of_pci_dma_configure() update dma configuration

On Monday 22 December 2014 17:40:30 Murali Karicheri wrote:
> On 12/22/2014 05:24 PM, Arnd Bergmann wrote:
> > On Monday 22 December 2014 16:40:43 Murali Karicheri wrote:
> >>>> +++ b/arch/arm/mm/dma-mapping.c
> >>>> @@ -2052,9 +2052,10 @@ void arch_setup_dma_ops(struct device *dev, u64
> >>>> dma_base, u64 size,
> >>>>                            struct iommu_ops *iommu, bool coherent)
> >>>>     {
> >>>>            struct dma_map_ops *dma_ops;
> >>>> +       u64 temp_size = min((*(dev->dma_mask) + 1), size);
> >>>>
> >>>>            dev->archdata.dma_coherent = coherent;
> >>>> -       if (arm_setup_iommu_dma_ops(dev, dma_base, size, iommu))
> >>>> +       if (arm_setup_iommu_dma_ops(dev, dma_base, temp_size, iommu))
> >>>>
> >>>> If you agree, I will post v1 of the patch with these updates. Let me
> >>>> know. I did some basic tests on Keystone with these changes and it works
> >>>> fine.
> >>>
> >>> It's not exactly what I meant. My main point was that we need to limit
> >>> dev->dma_mask to (size-1) here, but you are not touching that.
> >>
> >> if you mean overriding the dev->dma_mask to min((*dev->dma_mask),
> >> size-1), then I am getting the error "Coherent DMA mask 0x7fffffff (pfn
> >> 0x780000-0x800000) covers a smaller range of system memory than the DMA
> >> zone pfn 0x0-0x880000) when the devices on Keystone tries to set the dma
> >> mask. Something wrong and I need to look into the code.
> >
> > Right, it sounds like the offset was applied incorrectly at some point.
> >
> > What are the DMA zone size and the phys-offset?
> 2G and 0x8_0000_0000. This limit the usable DMA size to 2G on Keystone, 
> I believe you shouldn't be limiting the dma mask to size-1 in this case, 
> right? The DT setup the dma-range to have a size of 2G (0x80000000).

No, the problem is something else: the pfn range that we calculate for the
coherent DMA mask should have been 0x800000-0x880000, not 0x780000-0x800000,
so we would exactly match the ZONE_DMA.

	Arnd
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