Dne 02. 02. 24 v 9:00 Pavel Hofman napsal(a):
Dne 30. 01. 24 v 20:22 Pavel Hofman napsal(a):
Dne 30. 01. 24 v 13:30 Jaroslav Kysela napsal(a):
It looks like a way to go. The hdmi_mode can be set using ALSA
configuration use snd_config_search (with global config - snd_config
pointer) and snd_config_get_bool functions for that. The variable
may be
named like 'defaults.pcm.plug.iec958.hdmi_mode' or so (see alsa.conf).
That's interesting. IIUC such parameter would globally switch all plugs
instances to the hdmi_mode. Would a user-based ~/.asoundrc with such
variable be applied for the hard-coded plughw:XX device? Maybe it would
be enough for most use cases, eliminating the need for an app-specific
environment variable.
Or maybe a prioritized sequence
getenv('ALSA_PCM_PLUG_IEC958_HDMI_MODE')
-> snd_config_search('defaults.pcm.plug.iec958.hdmi_mode') could be
used.
We usually don't use getenv hacks for alsa-lib features. The global
configuration path can be redirected using ALSA_CONFIG_DIR and per
user (~/.asoundrc or $XDG_CONFIG_HOME/alsa/asoundrc) and per card
configurations (/var/lib/alsa/card#.conf.d) are also loaded from the
global alsa.conf file.
Perphaps, the iec958 plug code may include card number / card driver
name to the configuration tree lookup - like
'defaults.pcm.plug.iec958.0.hdmi_mode' or
'defaults.pcm.plug.iec958.vc4-hdmi.hdmi_mode' . With this extension,
this value can be set in global src/conf/cards/vc4-hdmi.conf for this
hw.
Actually, looking at pcm_iec958.c and the commit which introduced the
hdmi_mode param I am not sure the the hdmi_mode is of any value for
the plug plugin.
IIUC the hdmi_mode value gets used only if the status is
IEC958_AES0_NONAUDIO:
int single_stream = iec->hdmi_mode &&
(iec->status[0] & IEC958_AES0_NONAUDIO) &&
(channels == 8);
But the plug plugin would pass NULL as status_bits which in
snd_pcm_iec958_open will be replaced with default_status_bits:
static const unsigned char default_status_bits[] = {
IEC958_AES0_CON_EMPHASIS_NONE,
IEC958_AES1_CON_ORIGINAL | IEC958_AES1_CON_PCM_CODER,
0,
IEC958_AES3_CON_FS_NOTID, /* will be set in hwparams */
IEC958_AES4_CON_WORDLEN_NOTID /* will be set in hwparams */
};
Logically no IEC958_AES0_NONAUDIO bit is set in the default status bits.
IMO we can safely pass hdmi_mode=false to snd_pcm_iec958_open because
using plug for non-audio stream would not make sense anyway.
A patch related to the conversion could look like this, IMO.
===================================================================
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 1706857992580)
@@ -490,6 +490,20 @@
}
#endif
+#ifdef BUILD_PCM_PLUGIN_IEC958
+static int snd_pcm_plug_iec958_open(snd_pcm_t **pcmp, const char *name,
snd_pcm_format_t sformat, snd_pcm_t *slave, int close_slave)
+{
+ return snd_pcm_iec958_open(pcmp, name, sformat, slave, close_slave,
+ /* using default status bits defined in the iec958 plugin*/
+ NULL,
+ /* default preamble values as used in the iec958 plugin */
+ {0x08, 0x02, 0x04 /* Z, X, Y */},
+ /* hdmi_mode=0 because it is applied only for
IEC958_AES0_NONAUDIO which is not in the default status bits */
+ 0
+ );
+}
+#endif
+
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;
@@ -565,6 +579,12 @@
#ifdef BUILD_PCM_PLUGIN_ADPCM
case SND_PCM_FORMAT_IMA_ADPCM:
f = snd_pcm_adpcm_open;
+ break;
+#endif
+#ifdef BUILD_PCM_PLUGIN_IEC958
+ case SND_PCM_FORMAT_IEC958_SUBFRAME_LE:
+ case SND_PCM_FORMAT_IEC958_SUBFRAME_BE:
+ f = snd_pcm_plug_iec958_open;
break;
#endif
default:
===================================================================
Unfortunately I am afraid I do not understand fully the code in
snd_pcm_plug_hw_refine_schange which calls method
snd_pcm_plug_slave_format where the IEC958 formats should also be checked.
I am trying to understand the code logic in
snd_pcm_plug_hw_refine_cchange and snd_pcm_plug_hw_refine_schange as
there are no comments at all, to no avail.
Please what is the meaning of local variable f in this snippet of
snd_pcm_plug_hw_refine_cchange
https://github.com/alsa-project/alsa-lib/blob/2a736a0d2543f206fd2653aaae8a08a4c42eb917/src/pcm/pcm_plug.c#L909-L921
?
for (format = 0; format <= SND_PCM_FORMAT_LAST; format++) {
snd_pcm_format_t f;
if (!snd_pcm_format_mask_test(format_mask, format))
continue;
if (snd_pcm_format_mask_test(sformat_mask, format))
f = format;
else {
f = snd_pcm_plug_slave_format(format, sformat_mask);
if (f == SND_PCM_FORMAT_UNKNOWN)
continue;
}
snd_pcm_format_mask_set(&fmt_mask, format);
}
The snd_pcm_plug_hw_refine_schange method sets the f to the fmt_mask in
https://github.com/alsa-project/alsa-lib/blob/2a736a0d2543f206fd2653aaae8a08a4c42eb917/src/pcm/pcm_plug.c#L831
, but not in
https://github.com/alsa-project/alsa-lib/blob/2a736a0d2543f206fd2653aaae8a08a4c42eb917/src/pcm/pcm_plug.c#L920
Please what is the meaning/contract of the method
snd_pcm_plug_slave_format
https://github.com/alsa-project/alsa-lib/blob/2a736a0d2543f206fd2653aaae8a08a4c42eb917/src/pcm/pcm_plug.c#L252
? What is the relation between input format and output format?
Thanks a lot in advance.
