linux-kernel - Re: [PATCH v3 4/7] of: configure the platform device dma parameters

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Date:	Thu, 1 May 2014 09:16:12 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Grant Likely <grant.likely@...aro.org>,
	<linux-kernel@...r.kernel.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Grygorii Strashko <grygorii.strashko@...com>
Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters

On Thursday 01 May 2014 09:12 AM, Grant Likely wrote:
> On Wed, 30 Apr 2014 10:19:15 -0400, Santosh Shilimkar <santosh.shilimkar@...com> wrote:
>> Hi Grant,
>>
>> On Tuesday 29 April 2014 10:41 AM, Grant Likely wrote:
>>> On Thu, 24 Apr 2014 11:30:04 -0400, Santosh Shilimkar <santosh.shilimkar@...com> wrote:
>>>> Retrieve DMA configuration from DT and setup platform device's DMA
>>>> parameters. The DMA configuration in DT has to be specified using
>>>> "dma-ranges" and "dma-coherent" properties if supported.
>>>>
>>>> We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops
>>>> using "dma-coherent" device tree properties.
>>>>
>>>> The set_arch_dma_coherent_ops macro has to be defined by arch if
>>>> it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is
>>>> declared as nop.
>>>>
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> Cc: Russell King <linux@....linux.org.uk>
>>>> Cc: Arnd Bergmann <arnd@...db.de>
>>>> Cc: Olof Johansson <olof@...om.net>
>>>> Cc: Grant Likely <grant.likely@...aro.org>
>>>> Cc: Rob Herring <robh+dt@...nel.org>
>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>> Cc: Linus Walleij <linus.walleij@...aro.org>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>
>>>> ---
>>>>  drivers/of/platform.c       |   48 ++++++++++++++++++++++++++++++++++++++++---
>>>>  include/linux/dma-mapping.h |    7 +++++++
>>>>  2 files changed, 52 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>>>> index 48de98f..270c0b9 100644
>>>> --- a/drivers/of/platform.c
>>>> +++ b/drivers/of/platform.c
>>>> @@ -187,6 +187,50 @@ struct platform_device *of_device_alloc(struct device_node *np,
>>>>  EXPORT_SYMBOL(of_device_alloc);
>>>>  
>>>>  /**
>>>> + * of_dma_configure - Setup DMA configuration
>>>> + * @dev:	Device to apply DMA configuration
>>>> + *
>>>> + * Try to get devices's DMA configuration from DT and update it
>>>> + * accordingly.
>>>> + *
>>>> + * In case if platform code need to use own special DMA configuration,it
>>>> + * can use Platform bus notifier and handle BUS_NOTIFY_ADD_DEVICE event
>>>> + * to fix up DMA configuration.
>>>> + */
>>>> +static void of_dma_configure(struct device *dev)
>>>> +{
>>>> +	u64 dma_addr, paddr, size;
>>>> +	int ret;
>>>> +
>>>> +	dev->coherent_dma_mask = DMA_BIT_MASK(32);
>>>> +	if (!dev->dma_mask)
>>>> +		dev->dma_mask = &dev->coherent_dma_mask;
>>>> +
>>>> +	/*
>>>> +	 * if dma-coherent property exist, call arch hook to setup
>>>> +	 * dma coherent operations.
>>>> +	 */
>>>> +	if (of_dma_is_coherent(dev->of_node)) {
>>>> +		set_arch_dma_coherent_ops(dev);
>>>> +		dev_dbg(dev, "device is dma coherent\n");
>>>> +	}
>>>> +
>>>> +	/*
>>>> +	 * if dma-ranges property doesn't exist - just return else
>>>> +	 * setup the dma offset
>>>> +	 */
>>>> +	ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>>>> +	if ((ret == -ENODEV) || (ret < 0)) {
>>>> +		dev_dbg(dev, "no dma range information to setup\n");
>>>> +		return;
>>>> +	}
>>>> +
>>>> +	/* DMA ranges found. Calculate and set dma_pfn_offset */
>>>> +	dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
>>>> +	dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>>>
>>> I've got two concerns here. of_dma_get_range() retrieves only the first
>>> tuple from the dma-ranges property, but it is perfectly valid for
>>> dma-ranges to contain multiple tuples. How should we handle it if a
>>> device has multiple ranges it can DMA from?
>>>
>>
>> We've not found any cases in current Linux where more than one dma-ranges
>> would be used. Moreover, The MM (definitely for ARM) isn't supported such
>> cases at all (if i understand everything right).
>> - there are only one arm_dma_pfn_limit
>> - there is only one MM zone is used for ARM
>> - some arches like x86,mips can support 2 zones (per arch - not per device or bus)
>>   DMA & DMA32, but they configured once and forever per arch.
> 
> Okay. If anyone ever does implement multiple ranges then this code will
> need to be revisited.
>
Sure. Thanks for the review !!
 
Regards,
Santosh

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