From: Timo Wischer twischer@de.adit-jv.com

Without this patch it is not possible to link the channel and format parameter if snd_pcm_extplug_set_param_*() or snd_pcm_extplug_set_slave_param_*() is called. Therefore the client and slave parameter can differ. So the extplug has to implement conversion. To avoid this the new snd_pcm_extplug_set_param_link() function can be called. As a reproduction sceanrio the following extplug source code can be used: static snd_pcm_sframes_t my_transfer(snd_pcm_extplug_t *e, const snd_pcm_channel_area_t *da, snd_pcm_uframes_t dof, const snd_pcm_channel_area_t *sa, snd_pcm_uframes_t sof, snd_pcm_uframes_t s) { return s; } static const snd_pcm_extplug_callback_t my_own_callback = { .transfer = my_transfer }; SND_PCM_PLUGIN_DEFINE_FUNC(my_plug) { snd_config_iterator_t i, next; snd_config_t *slave = NULL; snd_pcm_extplug_t *myplug; snd_config_for_each(i, next, conf) { snd_config_t *n = snd_config_iterator_entry(i); const char *id; if (snd_config_get_id(n, &id) < 0) continue; if (strcmp(id, "comment") == 0 || strcmp(id, "type") == 0) continue; if (strcmp(id, "slave") == 0) { slave = n; continue; } return -EINVAL; } myplug = calloc(1, sizeof(*myplug)); myplug->version = SND_PCM_EXTPLUG_VERSION; myplug->callback = &my_own_callback; snd_pcm_extplug_create(myplug, name, root, slave, stream, mode);

snd_pcm_extplug_set_param_minmax(myplug, SND_PCM_EXTPLUG_HW_CHANNELS, 1, 16); // snd_pcm_extplug_set_param_link(myplug, SND_PCM_EXTPLUG_HW_CHANNELS, 1);

*pcmp = myplug->pcm; return 0; } SND_PCM_PLUGIN_SYMBOL(my_plug);

To use this plugin the following ALSA configuration is required: pcm.myplug { type my_plug slave.pcm hw:Dummy }

With this configuration without this patch snd_pcm_hw_params_get_channels_max() will always return 16 channels independent of the supported channels of the dummy device. Due to that for example the start up of JACK would fail: $ modprobe snd_dummy $ jackd -d alsa -P myplug ALSA: cannot set channel count to 16 for playback ALSA: cannot configure playback channel

Signed-off-by: Timo Wischer twischer@de.adit-jv.com

diff --git a/include/pcm_extplug.h b/include/pcm_extplug.h index ced934f..e5c02d4 100644 --- a/include/pcm_extplug.h +++ b/include/pcm_extplug.h @@ -184,6 +184,8 @@ int snd_pcm_extplug_set_param_list(snd_pcm_extplug_t *extplug, int type, unsigne int snd_pcm_extplug_set_param_minmax(snd_pcm_extplug_t *extplug, int type, unsigned int min, unsigned int max); int snd_pcm_extplug_set_slave_param_list(snd_pcm_extplug_t *extplug, int type, unsigned int num_list, const unsigned int *list); int snd_pcm_extplug_set_slave_param_minmax(snd_pcm_extplug_t *extplug, int type, unsigned int min, unsigned int max); +int snd_pcm_extplug_set_param_link(snd_pcm_extplug_t *extplug, int type, + int keep_link);

/** * set the parameter constraint with a single value diff --git a/src/pcm/pcm_ext_parm.h b/src/pcm/pcm_ext_parm.h index d25f2ab..7b99bef 100644 --- a/src/pcm/pcm_ext_parm.h +++ b/src/pcm/pcm_ext_parm.h @@ -5,6 +5,7 @@ struct snd_ext_parm { unsigned int *list; unsigned int active: 1; unsigned int integer: 1; + unsigned int keep_link: 1; };

static inline snd_mask_t *hw_param_mask(snd_pcm_hw_params_t *params, diff --git a/src/pcm/pcm_extplug.c b/src/pcm/pcm_extplug.c index 1f887c5..94002dc 100644 --- a/src/pcm/pcm_extplug.c +++ b/src/pcm/pcm_extplug.c @@ -249,7 +249,7 @@ static unsigned int get_links(struct snd_ext_parm *params) SND_PCM_HW_PARBIT_TICK_TIME);

for (i = 0; i < SND_PCM_EXTPLUG_HW_PARAMS; i++) { - if (params[i].active) + if (params[i].active && !params[i].keep_link) links &= ~excl_parbits[i]; } return links; @@ -642,6 +642,17 @@ as former functions. To clear the parameter constraints, call #snd_pcm_extplug_params_reset() function.

+When using snd_pcm_extplug_set_param_*() or snd_pcm_extplug_set_slave_param_*() +for any parameter. This parameter is no longer linked between the client and +slave PCM. Therefore it could differ and the extplug has to support conversion +between all valid parameter configurations. To keep the client and slave +parameter linked #snd_pcm_extplug_set_param_link() can be used for the +corresponding parameter. For example if the extplug does not support channel nor +format conversion the supported client parameters can be limited with +snd_pcm_extplug_set_param_*() and afterwards +#snd_pcm_extplug_set_param_link(ext, SND_PCM_EXTPLUG_HW_FORMAT, 1) and +#snd_pcm_extplug_set_param_link(ext, SND_PCM_EXTPLUG_HW_CHANNELS, 1) should be +called to keep the client and slave parameters the same. */

/** @@ -849,3 +860,26 @@ int snd_pcm_extplug_set_param_minmax(snd_pcm_extplug_t *extplug, int type, unsig return snd_ext_parm_set_minmax(&ext->params[type], min, max); }

+/** + * @brief Keep the client and slave format/channels the same if requested. This + * is for example useful if this extplug does not support any channel + * conversion. + * @param extplug the extplug handle + * @param type parameter type + * @param keep_link if 1 the parameter identified by type will be kept the same + * for the client and slave PCM of this extplug + * @return 0 if successful, or a negative error code + */ +int snd_pcm_extplug_set_param_link(snd_pcm_extplug_t *extplug, int type, + int keep_link) +{ + extplug_priv_t *ext = extplug->pcm->private_data; + + if (type < 0 || type >= SND_PCM_EXTPLUG_HW_PARAMS) { + SNDERR("EXTPLUG: invalid parameter type %d", type); + return -EINVAL; + } + ext->params[type].keep_link = keep_link ? 1 : 0; + ext->sparams[type].keep_link = keep_link ? 1 : 0; + return 0; +}