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Commit a690a2a1 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: Fix wrong description about hw constraints 



The definitions of hw constraint functions are wrongly placed, and the
description about the function is also wrong.
hw_rule_channels_by_format actually refines the channels depending on
the format, not vice versa.

Reported-by: default avatarPeter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 05dc0fc9

Documentation/DocBook/writing-an-alsa-driver.tmpl

+20 −19
Original line number Diff line number Diff line
@@ -3250,18 +3250,19 @@ struct _snd_pcm_runtime { 
	  <title>Example of Hardware Constraints for Channels</title>

	  <programlisting>

<![CDATA[

  static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,

  static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,

                                        struct snd_pcm_hw_rule *rule)

  {

          struct snd_interval *c = hw_param_interval(params,

                        SNDRV_PCM_HW_PARAM_CHANNELS);

          struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);

          struct snd_mask fmt;

          struct snd_interval ch;



          snd_mask_any(&fmt);    /* Init the struct */

          if (c->min < 2) {

                  fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;

                  return snd_mask_refine(f, &fmt);

          snd_interval_any(&ch);

          if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {

                  ch.min = ch.max = 1;

                  ch.integer = 1;

                  return snd_interval_refine(c, &ch);

          }

          return 0;

  }
@@ -3285,27 +3286,27 @@ struct _snd_pcm_runtime { 
      </para>



      <para>

        The rule function is called when an application sets the number of

        channels. But an application can set the format before the number of

        channels. Thus you also need to define the inverse rule:

        The rule function is called when an application sets the PCM

	format, and it refines the number of channels accordingly.

        But an application may set the number of channels before

	setting the format. Thus you also need to define the inverse rule:



       <example>

	 <title>Example of Hardware Constraints for Channels</title>

	 <title>Example of Hardware Constraints for Formats</title>

	 <programlisting>

<![CDATA[

  static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,

  static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,

                                        struct snd_pcm_hw_rule *rule)

  {

          struct snd_interval *c = hw_param_interval(params,

                SNDRV_PCM_HW_PARAM_CHANNELS);

          struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);

          struct snd_interval ch;

          struct snd_mask fmt;



          snd_interval_any(&ch);

          if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {

                  ch.min = ch.max = 1;

                  ch.integer = 1;

                  return snd_interval_refine(c, &ch);

          snd_mask_any(&fmt);    /* Init the struct */

          if (c->min < 2) {

                  fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;

                  return snd_mask_refine(f, &fmt);

          }

          return 0;

  }