[alsa-devel] hw_params function and OSS emulation

[Takashi Iwai]

At Wed, 22 Aug 2007 10:02:11 -0500,
Timur Tabi wrote:
> 
> Takashi Iwai wrote:
> 
> > Alternatively, you can remember the last allocated buffer-size and
> > re-use the same buffer if the requested size is less than it.
> > Since the buffer size change won't happen _so often_ (even via OSS
> > emulation), this would work well in practice, too.
> 
> Hmm... Neither of these options is really that great.

... but no other way :)  The buffer size is dynamically configurable,
per design.  That's all.

>  I think I like the idea 
> of pre-allocating the buffer in .new.  What is a reasonable maximum size for 
> the DMA buffer?  32KB seems small to me.

AFAIK, 64kB seems sufficient in most cases.

>  When I was testing OSS emulation, 
> the first call to .hw_params passed a DMA buffer size of over 1MB!

The driver should deny a too large size if it's unrealistic.
But 1MB is realistic for many systems.  So, the number depends on the
system.


Takashi