Dne 26. 01. 24 v 9:00 Pavel Hofman napsal(a):
RPi has recently moved to the VC4 driver which accepts only
IEC958_SUBFRAME_LE format
https://github.com/torvalds/linux/blob/ecb1b8288dc7ccbdcb3b9df005fa1c0e0c0388a7/drivers/gpu/drm/vc4/vc4_hdmi.c#L2643 . Since then people started to have issues with their previous configs which use only the plug plugin (plughw:X).
Wrapping the device with the hdmi plugin solves the problem, as it
should. But e.g. mainline java support for alsa offers only hw cards
wrapped with the plug plugin (hardcoded, not possible to specify the
device name directly). Stock Java apps then do not work with RPi HDMI.
I was wondering if it made sense to add support for the IEC958 formats
(using the iec958 plugin methods) to the plug plugin.
It may be complicated with the hdmi_mode hint though, I do not know if
there is any API to recognize HDMI vs. SPDIF. Maybe a different format
specifically for HDMI could have been perhaps useful but it may be too
late for that.
Thank you very much for consideration.
Perhaps something trivial like this could do (header file changes not
included):
===================================================================
diff --git a/src/pcm/pcm_plug.c b/src/pcm/pcm_plug.c
--- a/src/pcm/pcm_plug.c (revision ffed4f342678c31bf0b9edfe184be5f3de41603a)
+++ b/src/pcm/pcm_plug.c (date 1706546414549)
@@ -490,6 +490,14 @@
}
#endif
+int snd_pcm_plug_generic_iec958_open(snd_pcm_t **pcmp, const char
*name, snd_pcm_format_t sformat, snd_pcm_t *slave, int close_slave) {
+ unsigned char preamble_vals[3] = {
+ 0x08, 0x02, 0x04 /* Z, X, Y */
+ };
+ int hdmi_mode; // ????
+ return snd_pcm_iec958_open(pcmp, name, sformat, slave, close_slave,
NULL, preamble_vals, hdmi_mode);
+}
+
static int snd_pcm_plug_change_format(snd_pcm_t *pcm, snd_pcm_t **new,
snd_pcm_plug_params_t *clt, snd_pcm_plug_params_t *slv)
{
snd_pcm_plug_t *plug = pcm->private_data;
@@ -567,6 +575,10 @@
f = snd_pcm_adpcm_open;
break;
#endif
+ case SND_PCM_FORMAT_IEC958_SUBFRAME_LE:
+ case SND_PCM_FORMAT_IEC958_SUBFRAME_BE:
+ f = pcm_snd_general_iec958_open;
+ break;
default:
return -EINVAL;
}
===================================================================
IMO preamble_vals could be left at the same default as defined in
pcm_iec958.c:_snd_pcm_iec958_open().
But the correct hdmi_mode parameter is necessary. Alsa configs specify
it explicitly (like vc4-hdmi.conf). But the plug plugin has no such
information. Adding a parameter like that to the plug plugin would
cancel the effect of this change (to support hardcoded plughw devices
e.g. in java, with no support for custom PCM devices).
Maybe an environment variable could be defined for the whole application
which could be used for the hdmi_mode, an ugly hack though...
Thanks a lot for any hints and suggestions.
With regards,
Pavel.
