Re: [PATCH 2/2] arcmsr: code cleanup and some corrections

[Tomas Henzl <thenzl@redhat.com>]

On 02/18/2011 02:04 AM, FUJITA Tomonori wrote:
> On Thu, 17 Feb 2011 16:05:37 +0100
> Tomas Henzl <thenzl@redhat.com> wrote:
>
>   
>> the discussion is mostly if 'dma_alloc_coherent' 
>> ...
>> dma_coherent = dma_alloc_coherent(&pdev->dev, acb->uncache_size, &dma_coherent_handle, GFP_KERNEL);
>> ...
>> returns a page address - dma_coherent with last, I think five bits, zeroed.
>> Could you help us with that?
>>     
> Documentation/DMA-API-HOWTO.txt is not clear enough?
>
> =
> dma_alloc_coherent returns two values: the virtual address which you
> can use to access it from the CPU and dma_handle which you pass to the
> card.
>
> The cpu return address and the DMA bus master address are both
> guaranteed to be aligned to the smallest PAGE_SIZE order which
> is greater than or equal to the requested size.  This invariant
> exists (for example) to guarantee that if you allocate a chunk
> which is smaller than or equal to 64 kilobytes, the extent of the
> buffer you receive will not cross a 64K boundary.
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>   
It's clear enough I think, I asked this question because Nick doesn't
have a "100% confidence in that.". So I wanted a help to convince him.