[alsa-devel] aplay -l vs. aplay -L: Missing PCMs?

Stephen Warren swarren at nvidia.com
Fri Aug 20 19:08:45 CEST 2010

Jaroslav Kysela wrote:
> On Thu, 19 Aug 2010, Stephen Warren wrote:
> > The Azalia controller on NVIDIA GPUs gives 4 ALSA hw devices:
> >
> > (on card 1):
> >
> > [swarren at swarren-lx2 ~]$ sudo aplay -l
> > << includes hw=1,3 hw=1,7 hw=1,8 hw=1,9 >>
> > ... all of which appear to work OK.
> >
> > However, the list of available "PCMs" from aplay -L doesn't expose them all:
> >
> > [swarren at swarren-lx2 ~]$ sudo aplay -L
> > <<card 0 "Nvidia" elided>>
> > hdmi:CARD=NVidia_1
> >    HDA NVidia, NVIDIA HDMI
> >    HDMI Audio Output
> >
> > Instead, I imagined that I'd see 4 PCMs listed by "aplay -L"; one for each
> > converter. Is this an incorrect assumption? How would I make that happen?
> There is a bug in alsa-lib to namehint.c. The code assumes that hw device
> number is similar to logical device numbers which is not true in case of
> your HDMI devices:
> 3, 7, 8, 9
> The fallback code is used and only first logical device 0 is created.
> Could you test this patch?
> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=97d25c0766405453d3c298bd51dd4916121a4f6a

I tested that, and unfortunately it doesn't seem to work; I get the exact same
aplay -L output.

I debugged this a little, and see that add_card() is calculating the correct
max_devices value for card=1 str=hdmi. However, in the loop that right after
that calls try_config, when device=0, it returns 0, but when device=1, it
returns -2 (-ENOENT). This happens inside try_config where it calls
snd_config_search_definition (line 244 in latest git). At that point, buf is:


... which seems reasonable.

I'm a little confused about the device numbering though: The max_devices
value is counting values "3, 7, 8, 9" and hence gets 9. However, the loop that
calls try_config loops 0..max_devices-1, but bails out as soon as any error is
found, thus disallowing "holes" in the numbering. That implies that "device" in
that loop is a different numbering space? After I noticed that, I hacked that
loop to continue instead of break on errors, and also removed the "err >= 0"
condition from the loop, expecting that when device==3/7/8/9, try_config might
work. In fact, 0 still works (of course) and 1..8 all fail with err=-2, so I
assume at the same place in try_config.


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