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Date:	Mon, 22 Dec 2014 16:40:43 -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 12/22/2014 02:43 PM, Arnd Bergmann wrote:
> On Monday 22 December 2014 12:46:12 Murali Karicheri wrote:
>> 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.
>>>> +	/*
>>>> +	 * 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;
>
> Right.
>
>>>> +	} 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.
>
> 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.

> either change the two functions in which we first assign the dma_mask
> (platform and pci bus), or set it again in arch_setup_dma_ops (on each
> architecture implementing it), either way would work. Someone else
> might have a stronger opinion on that matter.
>
> For arm_setup_iommu_dma_ops, passing the original size is probably
> best.
>
> 	Arnd


-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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