[PATCH V3] of: Set the DMA mask to 64 bits when dma_addr_t is 64-bits
tom.leiming at gmail.com
Wed Jul 3 10:15:50 EDT 2013
On Sat, Apr 27, 2013 at 5:32 AM, Rob Herring <robherring2 at gmail.com> wrote:
> On 04/26/2013 03:31 PM, Laura Abbott wrote:
>> Currently, of_platform_device_create_pdata always sets the
>> coherent DMA mask to 32 bits. On ARM systems without CONFIG_ZONE_DMA,
>> arm_dma_limit gets set to ~0 or 0xFFFFFFFFFFFFFFFF on LPAE based
>> systems. Since arm_dma_limit represents the smallest dma_mask
>> on the system, the default of 32 bits prevents any dma_coherent
>> allocation from succeeding unless clients manually set the
>> dma mask first. Rather than make every client on an LPAE system set
>> the mask manually, account for the size of dma_addr_t when setting
>> the coherent mask.
>> Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
>> drivers/of/platform.c | 2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> index 0970505..5f0ba94 100644
>> --- a/drivers/of/platform.c
>> +++ b/drivers/of/platform.c
>> @@ -214,7 +214,7 @@ struct platform_device *of_platform_device_create_pdata(
>> #if defined(CONFIG_MICROBLAZE)
>> dev->archdata.dma_mask = 0xffffffffUL;
>> - dev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
>> + dev->dev.coherent_dma_mask = DMA_BIT_MASK(sizeof(dma_addr_t) * 8);
> This is going to change the mask from 32 to 64 bits on 64-bit powerpc
> and others possibly. Maybe it doesn't matter. I think it doesn't, but
> I'm not sure enough to apply for 3.10. So I'll queue it for 3.11.
Without the patch, LPAE enabled board may not boot at all, but looks
it still isn't in -next tree.
But I am wondering if it is a correct approach, because enabling LPAE
doesn't mean the I/O devices can support DMA to/from 64bit address, and
it is very probably devices can't do it at all.
Another way is to always set arm_dma_limit as 0xFFFFFFFF when
CONFIG_ZONE_DMA is unset, and let driver override device's dma
mask if the device supports 64bit DMA.
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