Re: [alsa-devel] [PATCH] 6fire: fix URB transfer buffer for midi output

[Takashi Iwai <tiwai-l3A5Bk7waGM@public.gmane.org>]

At Thu, 08 Aug 2013 09:16:27 +0200,
Clemens Ladisch wrote:
> 
> Takashi Iwai wrote:
> > Alan Stern wrote:
> >> A buffer _can_ be in the middle of a kmalloc'ed space, but the CPU must
> >> not access any of the fields around it that might occupy the same cache
> >> line while the buffer is being used for DMA.
> >
> > Hrm, but does the kmalloc buffer always guarantee such cache line
> > exclusiveness...?  I thought a simple one like SLOB doesn't care.
> 
> Documentation/DMA-API-HOWTO.txt says:
> |  Architectures must ensure that kmalloc'ed buffer is
> |  DMA-safe. Drivers and subsystems depend on it. If an architecture
> |  isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in
> |  the CPU cache is identical to data in main memory),
> |  ARCH_DMA_MINALIGN must be set so that the memory allocator
> |  makes sure that kmalloc'ed buffer doesn't share a cache line with
> |  the others.

Ah, good, thanks!


Takashi
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