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author | Takashi Iwai <tiwai@suse.de> | 2013-02-05 12:24:22 +0100 |
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committer | Takashi Iwai <tiwai@suse.de> | 2013-02-05 12:24:22 +0100 |
commit | a690a2a1eb32e533e2b2afb1daeef3c4011d47e9 (patch) | |
tree | f0c0cdf087f6922448db96cf222122aa443de4b1 /Documentation/DocBook/writing-an-alsa-driver.tmpl | |
parent | 05dc0fc9d01537a66d9a0cffe2e96296d8f4c7ac (diff) | |
download | linux-a690a2a1eb32e533e2b2afb1daeef3c4011d47e9.tar.bz2 |
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: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/DocBook/writing-an-alsa-driver.tmpl')
-rw-r--r-- | Documentation/DocBook/writing-an-alsa-driver.tmpl | 39 |
1 files changed, 20 insertions, 19 deletions
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl index c0781bb1f9b5..c564faab981c 100644 --- a/Documentation/DocBook/writing-an-alsa-driver.tmpl +++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl @@ -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); + 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); + 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; } |