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pcm: extplug: Keep format and channels the same if requested

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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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Timo Wischer 2018-12-10 11:33:16 +01:00 • committed by Takashi Iwai
parent c9fcf98369
commit ee64b4b83a
3 changed files with 38 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

2
include/pcm_extplug.h
View file

@ -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

1
src/pcm/pcm_ext_parm.h
View file

@ -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,

36
src/pcm/pcm_extplug.c
View file

@ -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;
}