linux-kernel - Re: [PATCH v2 4/7] of: configure the platform device dma parameters

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Message-ID: <53568641.2020300@ti.com>
Date:	Tue, 22 Apr 2014 18:09:53 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Rob Herring <robherring2@...il.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.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>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 4/7] of: configure the platform device dma parameters

Hi Rob,

On 04/21/2014 05:58 PM, Rob Herring wrote:
> On Sat, Apr 19, 2014 at 9:32 AM, 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       |   43 +++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/dma-mapping.h |    7 +++++++
>>   2 files changed, 50 insertions(+)
>>
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index 573db15..7e4a43b 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -187,6 +187,47 @@ 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)
>> +{
>> +       dma_addr_t dma_addr;
>> +       phys_addr_t paddr, size;
> 
> A problem with using dma_addr_t and phys_addr_t is that they normally
> depend on CONFIG_LPAE, but the address cell sizes are independent of
> that. That is why all the memory related functions stick with u64. I
> think you would have issues here if you have a platform with sizes of
> 4GB or more. You need to properly cap the sizes and addresses.
> 
>> +       int ret;
>> +
>> +       /*
>> +        * 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 < 0) {
> 
> Perhaps an error is not the right return for the default case. The
> default should probably be dma_addr and paddr equal to 0 and size 4GB.

The error code is needed here to properly distinguish the case when 
there are no "dma-ranges" defined in DT. Also, I think, that 
of_dma_get_range() shouldn't return any default values - It just
has to get data from DT. And the caller should decide what to do
with this data and how to handle error cases.

So, I prefer to keep behavior as is:
- in case of failure of_dma_get_range() will not touch values of
  &dma_addr, &paddr, &size.

> 
>> +               dev_dbg(dev, "no dma range information to setup\n");
>> +               return;
>> +       } else {
> 
> You don't need the else here.
> 

[...]

Thanks for your comments.

Regards,
-Grygorii

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