[pulseaudio-discuss] [PATCH v2 1/3] alsa: Add "exact-channels" mapping configurability

[Raymond Yau]

>
> Allow a mapping to relax the exact channel restriction:
>
> exact-channels = yes | no # If no, and the exact number of channels is
not supported,
>                           # allow device to be opened with another
channel count

Do you mean user have to define the mapping since these kind of devices
usually support only playback channels >= 10 (even number) and capture
channels >= 4 and does not support stereo ?

What happen when user define a mapping of an odd number of channels which
is not supported by the sound card ?

> ---
>  src/modules/alsa/alsa-mixer.c                    | 43
+++++++++++++++++++++---
>  src/modules/alsa/alsa-mixer.h                    |  1 +
>  src/modules/alsa/mixer/profile-sets/default.conf |  2 ++
>  3 files changed, 42 insertions(+), 4 deletions(-)
>
> diff --git a/src/modules/alsa/alsa-mixer.c b/src/modules/alsa/alsa-mixer.c
> index 58f9182..77c3c7e 100644
> --- a/src/modules/alsa/alsa-mixer.c
> +++ b/src/modules/alsa/alsa-mixer.c
> @@ -3368,6 +3368,7 @@ pa_alsa_mapping
*pa_alsa_mapping_get(pa_alsa_profile_set *ps, const char *name)
>
>      m = pa_xnew0(pa_alsa_mapping, 1);
>      m->profile_set = ps;
> +    m->exact_channels = true;
>      m->name = pa_xstrdup(name);
>      pa_sample_spec_init(&m->sample_spec);
>      pa_channel_map_init(&m->channel_map);
> @@ -3485,6 +3486,30 @@ static int
mapping_parse_paths(pa_config_parser_state *state) {
>      return 0;
>  }
>
> +static int mapping_parse_exact_channels(pa_config_parser_state *state) {
> +    pa_alsa_profile_set *ps;
> +    pa_alsa_mapping *m;
> +    int b;
> +
> +    pa_assert(state);
> +
> +    ps = state->userdata;
> +
> +    if (!(m = pa_alsa_mapping_get(ps, state->section))) {
> +        pa_log("[%s:%u] %s invalid in section %s", state->filename,
state->lineno, state->lvalue, state->section);
> +        return -1;
> +    }
> +
> +    if ((b = pa_parse_boolean(state->rvalue)) < 0) {
> +        pa_log("[%s:%u] %s has invalid value '%s'", state->filename,
state->lineno, state->lvalue, state->section);
> +        return -1;
> +    }
> +
> +    m->exact_channels = b;
> +
> +    return 0;
> +}
> +
>  static int mapping_parse_element(pa_config_parser_state *state) {
>      pa_alsa_profile_set *ps;
>      pa_alsa_mapping *m;
> @@ -4156,6 +4181,7 @@ pa_alsa_profile_set* pa_alsa_profile_set_new(const
char *fname, const pa_channel
>          { "element-input",          mapping_parse_element,        NULL,
NULL },
>          { "element-output",         mapping_parse_element,        NULL,
NULL },
>          { "direction",              mapping_parse_direction,      NULL,
NULL },
> +        { "exact-channels",         mapping_parse_exact_channels, NULL,
NULL },
>
>          /* Shared by [Mapping ...] and [Profile ...] */
>          { "description",            mapping_parse_description,    NULL,
NULL },
> @@ -4264,10 +4290,12 @@ static void
profile_finalize_probing(pa_alsa_profile *to_be_finalized, pa_alsa_p
>  static snd_pcm_t* mapping_open_pcm(pa_alsa_mapping *m,
>                                     const pa_sample_spec *ss,
>                                     const char *dev_id,
> +                                   bool exact_channels,
>                                     int mode,
>                                     unsigned default_n_fragments,
>                                     unsigned default_fragment_size_msec) {
>
> +    snd_pcm_t* handle;
>      pa_sample_spec try_ss = *ss;
>      pa_channel_map try_map = m->channel_map;
>      snd_pcm_uframes_t try_period_size, try_buffer_size;
> @@ -4279,10 +4307,17 @@ static snd_pcm_t*
mapping_open_pcm(pa_alsa_mapping *m,
>          pa_frame_size(&try_ss);
>      try_buffer_size = default_n_fragments * try_period_size;
>
> -    return pa_alsa_open_by_template(
> +    handle = pa_alsa_open_by_template(
>                                m->device_strings, dev_id, NULL, &try_ss,
>                                &try_map, mode, &try_period_size,
> -                              &try_buffer_size, 0, NULL, NULL, true);
> +                              &try_buffer_size, 0, NULL, NULL,
exact_channels);
> +    if (handle && !exact_channels && m->channel_map.channels !=
try_map.channels) {
> +        char buf[PA_CHANNEL_MAP_SNPRINT_MAX];
> +        pa_log_debug("Channel map for mapping '%s' permanently changed
to '%s'", m->name,
> +                     pa_channel_map_snprint(buf, sizeof(buf), &try_map));
> +        m->channel_map = try_map;
> +    }
> +    return handle;
>  }
>
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