[alsa-devel] [PATCH] ASoC: omap-pcm: Lower the dma coherent mask to 32bits

[Takashi Iwai]

At Fri, 6 Dec 2013 12:25:43 +0000,
Russell King - ARM Linux wrote:
> 
> On Fri, Dec 06, 2013 at 09:12:22AM +0100, Takashi Iwai wrote:
> > But, it's still unclear why only get_coherent_dma_mask() takes max_pfn
> > into account for the check of dma_to_pfn(dev, mask).
> > 
> > In dma_supported(), 
> > 
> > 	unsigned long limit;
> > 	limit = dma_to_pfn(dev, mask);
> > 	if (limit < arm_dma_pfn_limit)
> > 		return 0;
> > 
> > while in get_coherent_dma_mask(),
> > 
> > 	unsigned long max_dma_pfn;
> > 	max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
> > 	if (dma_to_pfn(dev, mask) < max_dma_pfn)
> > 		return 0;
> > 
> > So, the current code looks to me that the results from
> > dma_set_coherent_mask() and the actual allocation may conflict.
> 
> I did ask Peter to replace *both* with the same thing.

Well, I'm looking at different points.  You requested Peter to test
both functions to take:

 	if (sizeof(mask) != sizeof(dma_addr_t) &&
 	    mask > (dma_addr_t)~0 &&
 	    dma_to_pfn(dev, ~0) < min(max_pfn, arm_dma_pfn_limit))
		return 0;

But, after that line, dma_supported() has another check:

 	if (dma_to_pfn(dev, mask) < arm_dma_pfn_limit)
 		return 0;

and get_coherent_dma_mask() has a different check:

 	if (dma_to_pfn(dev, mask) < min(max_pfn, arm_dma_pfn_limit))
 		return 0;

(the expressions here are expanded for easier comparison)

This is what I'm wondering.


Takashi