[alsa-devel] Maximum buffer size on HDA

[Takashi Iwai]

At Mon, 16 Jun 2008 12:53:11 +0200 (CEST),
Jaroslav Kysela wrote:
> 
> On Mon, 16 Jun 2008, Takashi Iwai wrote:
> 
> > At Fri, 13 Jun 2008 21:13:03 +0200,
> > Lennart Poettering wrote:
> > > 
> > > Heya,
> > > 
> > > the HDA driver allows a playback buffer size of something like 64K
> > > onyl. Is this a driver limitation or a limitation of the hardware?
> > > Skimming through the docs I cannot see anything like this, and I got
> > > the idea that the audio buffer is maintained in system memory, not
> > > sound card memory, so why this limit?
> > 
> > This comes from the buffer pre-allocator.
> > Run the below:
> > 
> > 	# echo 1024 > /proc/asound/card0/pcm0p/sub0/prealloc
> > 
> > then you can use now 1MB buffer.  snd-hda-intel has max
> > pre-allocation buffer size 1MB, and this is the hard-coded limit.
> > 
> > It's rather a silly constraint, and I think it'd be better cut off.
> > OTOH, this makes the system safer (e.g. avoiding page allocations for
> > too large buffers), and there is a proper workaround, too.
> > So, I'm open about this change, so far.
> 
> Which workaround you're talking about?

Reset a proc file manually like the above.  Without this, you cannot
allocate the buffer over the pre-allocated size.


Takashi