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

[Clemens Ladisch <clemens@ladisch.de>]

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.


Regards,
Clemens