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Date:	Mon, 22 Dec 2014 12:46:12 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>
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 12/18/2014 05:29 PM, Arnd Bergmann wrote:
> On Thursday 18 December 2014 17:07:04 Murali Karicheri wrote:
>> Add of_pci_dma_configure() to allow updating the dma configuration
>> of the pci device using the configuration from the parent of
>> the root bridge device.
>>
>> Signed-off-by: Murali Karicheri<m-karicheri2@...com>
>
> Much better!
>
> There is one detail that we should get right from the start here,
> which is currently wrong in the platform device code, but I have so
> far not dared change it:
>
>> +	/*
>> +	 * Set default dma-mask to 32 bit. Drivers are expected to setup
>> +	 * the correct supported dma_mask.
>> +	 */
>> +	dev->coherent_dma_mask = DMA_BIT_MASK(32);
>
> The 32-bit mask is indeed correct as the default for almost all cases,
> and we must not set it larger than DMA_BIT_MASK(32). There is one
> corner case though, which happens on some shmobile machines that have
> a 31-bit mask on the PCI host, and I think we should use that as the
> default.
>
>> +	/*
>> +	 * Set it to coherent_dma_mask by default if the architecture
>> +	 * code has not set it.
>> +	 */
>> +	if (!dev->dma_mask)
>> +		dev->dma_mask =&dev->coherent_dma_mask;
>> +
>> +	ret = of_dma_get_range(parent_np,&dma_addr,&paddr,&size);
>> +	if (ret<  0) {
>> +		dma_addr = offset = 0;
>> +		size = dev->coherent_dma_mask;
>
> Can you check one thing here? I believe the size argument as returned
> from of_dma_get_range is inclusive (e.g. 0x100000000), while the coherent
> mask by definition is exlusive (e.g. 0xffffffff), so the size needs to
> be adapted here. I haven't checked all the code here though, so I may
> be wrong.

size returned by of_dma_get_range() is inclusive as you indicated. Fromt 
the grep of dma-ranges in arch/arm/boot/dts, I see

arch/arm/boot/dts/keystone.dtsi:		dma-ranges = <0x80000000 0x8 
0x00000000 0x80000000>;
arch/arm/boot/dts/keystone.dtsi:			dma-ranges;
arch/arm/boot/dts/r8a7790.dtsi:		dma-ranges = <0x42000000 0 0x40000000 0 
0x40000000 0 0x80000000
arch/arm/boot/dts/integratorap.dts:	dma-ranges = <0x80000000 0x0 
0x80000000>;
arch/arm/boot/dts/r8a7791.dtsi:		dma-ranges = <0x42000000 0 0x40000000 0 
0x40000000 0 0x80000000

So I guess I need to change the code to

 >> +	ret = of_dma_get_range(parent_np,&dma_addr,&paddr,&size);
 >> +	if (ret<  0) {
 >> +		dma_addr = offset = 0;
 >> +		size = dev->coherent_dma_mask + 1;

>
>> +	} else {
>> +		offset = PFN_DOWN(paddr - dma_addr);
>> +		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>> +	}
>> +	dev->dma_pfn_offset = offset;
>> +
>> +	coherent = of_dma_is_coherent(parent_np);
>> +	dev_dbg(dev, "device is%sdma coherent\n",
>> +		coherent ? " " : " not ");
>> +
>> +	arch_setup_dma_ops(dev, dma_addr, size, NULL, coherent);
>
> Basically, I would use limit the size argument we pass into
> arch_setup_dma_ops to the minimum of 'size' and 'dma_mask' here,
> after converting into the same format. We should make sure we do the
> same thing for platform_device as well, so it might be better to do
> it inside of arch_setup_dma_ops instead.

Do you think following changes will work?

+++ 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.

Murali

>
> 	Arnd


-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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