On Tue, 18 Mar 2003, Laurent Canet wrote:
> Hi,
>
> On the HPPA architecture, devices (including sound ones) are memory-mapped.
> On particular machines, memory access to devices are not consistent,
> i.e. data wrote to memory could be cached by the CPU, thus inacessible
> to the device.
> To avoid inconsistency in memory writes, there are arch-dep functions
> that flush write buffers. They are defined in <asm/io.h> as
> dma_cache_inv(start,size), dma_cache_wback and dma_cache_wback_inv; and should be
> called after all DMA memory writes.
>
> On architectures that don't have such cache issues (most ia32, ia64, alpha, mips,
> ppc, ...), they are just NOP.
>
> I grepped out the whole alsa source tree and didn't find any occurences
> of dma_cache_* functions. Who should implement these calls, low level drivers or PCM
> middle layer ?
This code belongs to both midlevel and lowlevel drivers. See
snd_pcm_lib_*_transfer() routines in pcm_lib.c.
Also, we'll probably need to define these functions in our library,
because we can access directly to DMA ring buffers there, too.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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