[alsa-devel] link between HDMI ELD and PCM devices

[Takashi Iwai]

At Wed, 21 Sep 2011 08:44:15 +0200,
David Henningsson wrote:
> 
> On 09/21/2011 02:58 AM, Pierre-Louis Bossart wrote:
> >
> >>> There is some existing code such as pin_nid_to_pin_index() in
> >>> patch_hdmi.c, but I can't figure out what this pin_idx is, and how to
> >>> find the related PCM device number.
> >>> Any suggestions?
> >>
> >> That function simply returns the index into the array spec->pins[] that
> >> refers to that pin NID.
> >>
> >> Judging by hinfo_to_pin_index() (e.g. used near the start ofhdmi_pcm_open),
> >> that same index is valid  for spec->pcm_rec[] too, which I assume will
> >> give you access to what you want, possibly through the .stream[0] field.
> >
> > Looks like the device number is assigned in hda_codec.c and there's no
> > hooks to create the ELD control then...
> > Instead of creating a PCM_IFACE control, it's probably simpler to create
> > a MIXER control in the build_pcms routines, using the same name for the
> > control and the device, eg:
> >
> >> amixer -c0 controls
> > numid=1,iface=MIXER,name='ELD HDMI 0'
> >> aplay -l
> > card 0: Intel [HDA Intel], device 3: HDMI 0 [HDMI 0]
> >
> > That looks simple enough for apps to figure out which ELD control to
> > use? Feedback welcome.
> 
> This won't work - in the case of several HDMI codecs (common with 
> NVidia) there will be more than one "HDMI 0".
> 
> The solution is to actually find the device number out, like this:
> 
> 	struct hdmi_spec *spec = codec->spec;
> 	int pcmdev = spec->pcm_rec[pin_idx].device;
> 
> (This must be run after build_pcms, e g in build_controls.)

Yes, currently a device-number assignment is somehow tricky, as
it's assigned semi-dynamically.  But the method above David mentioned
should work.


thanks,

Takashi