RE: [PATCHv8 04/10] ARM: dma-mapping: remove offset parameter to prepare for generic dma_ops

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi Arnd,

On Wednesday, April 11, 2012 2:19 PM Arnd Bergmann wrote:

> On Wednesday 11 April 2012, Marek Szyprowski wrote:
> > Well, range sync functions are available from the early days of the dma
> > mapping api (at least that's what I've found reading the change log and
> > old patches). They are the correct way of doing a partial syncs on the
> > buffer (usually used by the network device drivers). This patch changes
> > only the internal implementation of the dma bounce functions to let
> > them tunnel through dma_map_ops structure. The driver api stays
> > unchanged, so driver are obliged to call dma_*_range_* functions to
> > keep code clean and easy to understand.
> >
> > The only drawback I can see from this patch is reduced detection of
> > the dma api abuse. Let us consider the following code:
> >
> > dma_addr = dma_map_single(dev, ptr, 64, DMA_TO_DEVICE);
> > dma_sync_single_range_for_cpu(dev, dma_addr+16, 0, 32, DMA_TO_DEVICE);
> >
> > Without the patch such code fails, because dma bounce code is unable
> > to find the bounce buffer for the given dma_address. After the patch
> > the sync call will be equivalent to:
> >
> >         dma_sync_single_range_for_cpu(dev, dma_addr, 16, 32, DMA_TO_DEVICE);
> >
> > which succeeds.
> >
> > I don't consider this as a real problem. DMA API abuse should be caught
> > by debug_dma_* function family, so we can simplify the internal low-level
> > implementation without losing anything.
> >
> 
> Ok, fair enough. Can you put the above text into the changelog?

Yes, I will update it in the next release.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>