Re: [PATCH v2 5/7] ARM: of: introduce common routine for DMA configuration

[Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Fri, Feb 28, 2014 at 6:00 PM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
> On Thursday 27 February 2014 16:17:50 Santosh Shilimkar wrote:
>> diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
>> index f751714..926b5dd 100644
>> --- a/arch/arm/kernel/devtree.c
>> +++ b/arch/arm/kernel/devtree.c
>> @@ -235,3 +238,61 @@ const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)
>>
>>       return mdesc;
>>  }
>> +
>> +void arm_dt_dma_configure(struct device *dev)
>> +{
>> +     dma_addr_t dma_addr;
>> +     phys_addr_t paddr, size;
>> +     dma_addr_t dma_mask;
>> +     int ret;
>> +
>> +     /*
>> +      * if dma-ranges property doesn't exist - use 32 bits DMA mask
>> +      * by default and don't set skip archdata.dma_pfn_offset
>> +      */
>> +     ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>> +     if (ret == -ENODEV) {
>> +             dev->coherent_dma_mask = DMA_BIT_MASK(32);
>> +             if (!dev->dma_mask)
>> +                     dev->dma_mask = &dev->coherent_dma_mask;
>> +             return;
>> +     }
>
> I think this is a reasonable default, but I also want Russell's
> opinion on this, since I suspect he will argue that we shouldn't
> default to setting a DMA mask for devices that are not DMA capable.

of_platform_device_create_pdata() in drivers/of/platform.c
does the same assumption since ages.

> Maybe someone has an idea how we can detect all three important cases:
>
> a) A device is marked as DMA capable using a dma-ranges property
> b) A device is known not to be DMA capable
> c) we don't have any dma-ranges properties in an old dtb file
>    but still want 32 bit masks by default.

The exact same solution would apply to the of core right?

Yours,
Linus Walleij
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