[alsa-devel] [PATCH] ALSA: hda - hdmi: Fallback to ALSA allocation when selecting CA

[Takashi Iwai]

At Mon, 02 Sep 2013 17:14:02 +0300,
Anssi Hannula wrote:
> 
> 02.09.2013 16:06, Takashi Iwai kirjoitti:
> > At Sun,  1 Sep 2013 14:36:47 +0300,
> > Anssi Hannula wrote:
> >> BTW, the hdmi_channel_allocation() logic seems also otherwise somewhat
> >> suspect to me. Shouldn't we always select an allocation matching ALSA
> >> channel mapping, instead of re-assigning channels received from
> >> userspace "randomly" to sink speakers (in case of unusual sink speaker
> >> mask)?
> > 
> > If per_pin->chmap_set is set beforehand,
> > hdmi_manual_channel_allocation() is called instead.  So it should be
> > fine.
> 
> I was talking about the "non-chmap" case.
> 
> Example:
> 
> Sink has FL + FR + FC + LFE.
> 
> Application plays 4 channel audio via ALSA, i.e. FL + FR + RL + RR as
> per ALSA API channel allocation.
> 
> Instead of sending CA for FL + FR + RL + RR (0x06) which is what the
> audio really is, hdmi_channel_allocation() selects CA for  FL + FR + FC
> + LFE (0x03), since that is what the sink reported as present. As a
> result rear channels are mapped to FC and LFE.
> 
> 
> Of course this is rather unusual case (in terms of sink speaker mask),
> and it may be argued that the user actually _wanted_ to output the
> second pair of channels to FC+LFE despite them normally being RL+RR in ALSA.

Yeah, of course, it's just a best effort and the channel map is
incomplete and might mismatch unless you explicitly set the channel
map.  This was the very reason we introduced this new API...


Takashi

> 
> 
> 
> > Takashi
> > 
> >> Anyway, I let it be for now at least.
> >>
> >>
> >>  sound/pci/hda/patch_hdmi.c | 11 +++++++++++
> >>  1 file changed, 11 insertions(+)
> >>
> >> diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
> >> index 030ca86..354fc55 100644
> >> --- a/sound/pci/hda/patch_hdmi.c
> >> +++ b/sound/pci/hda/patch_hdmi.c
> >> @@ -551,6 +551,17 @@ static int hdmi_channel_allocation(struct hdmi_eld *eld, int channels)
> >>  		}
> >>  	}
> >>  
> >> +	if (!ca) {
> >> +		/* if there was no match, select the regular ALSA channel
> >> +		 * allocation with the matching number of channels */
> >> +		for (i = 0; i < ARRAY_SIZE(channel_allocations); i++) {
> >> +			if (channels == channel_allocations[i].channels) {
> >> +				ca = channel_allocations[i].ca_index;
> >> +				break;
> >> +			}
> >> +		}
> >> +	}
> >> +
> >>  	snd_print_channel_allocation(eld->info.spk_alloc, buf, sizeof(buf));
> >>  	snd_printdd("HDMI: select CA 0x%x for %d-channel allocation: %s\n",
> >>  		    ca, channels, buf);
> >> -- 
> >> 1.8.1.5
> >>
> 
> 
> -- 
> Anssi Hannula
>