[alsa-devel] [PATCH] [v2] ASoC: support all possible sample rates in the WM8776 driver

[Takashi Iwai]

At Fri, 16 Sep 2011 09:16:54 -0500,
Timur Tabi wrote:
> 
> The .set_sysclk() function in ASoC codec drivers can be used to tell the
> driver what the frequency of master clock (mclk) is.  Some codecs use a
> divider on this clock to determine the sample rate.  The WM8776 is one such
> codec.
> 
> So instead of hard-coding a list of specific sample rates supported, these
> codec drivers can specify SNDRV_PCM_RATE_CONTINUOUS instead, clamping the
> range to the absolute limits of the hardware.  Then the .hw_params() function
> can use the mclk rate to determine whether any requested rate is actually
> supported.
> 
> Although the WM8776 driver includes a .set_sysclk function, it was also
> hard-coding the list of supported sample rates.  We change the hard-coded
> list to a range within the capabilities of the WM8776 itself.

It's not optimal from some aspects.  Basically this should be resolved
in hw_constraints, not in hw_params, so that the configurator can find
the possible rates.  Otherwise you have no idea what rate would be
accepted.

Since a few other codecs need the similar constraint, it may make
sense to have a common helper hw_constraint for such a case.


thanks,

Takashi

> 
> Signed-off-by: Timur Tabi <timur at freescale.com>
> ---
>  sound/soc/codecs/wm8776.c |   13 ++++++-------
>  1 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/sound/soc/codecs/wm8776.c b/sound/soc/codecs/wm8776.c
> index ad6f0fa..ca8a593 100644
> --- a/sound/soc/codecs/wm8776.c
> +++ b/sound/soc/codecs/wm8776.c
> @@ -321,11 +321,6 @@ static int wm8776_set_bias_level(struct snd_soc_codec *codec,
>  	return 0;
>  }
>  
> -#define WM8776_RATES (SNDRV_PCM_RATE_32000 | SNDRV_PCM_RATE_44100 |\
> -		      SNDRV_PCM_RATE_48000 | SNDRV_PCM_RATE_88200 |\
> -		      SNDRV_PCM_RATE_96000)
> -
> -
>  #define WM8776_FORMATS (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S20_3LE |\
>  			SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S32_LE)
>  
> @@ -350,7 +345,9 @@ static struct snd_soc_dai_driver wm8776_dai[] = {
>  			.stream_name = "Playback",
>  			.channels_min = 2,
>  			.channels_max = 2,
> -			.rates = WM8776_RATES,
> +			.rates = SNDRV_PCM_RATE_CONTINUOUS,
> +			.rate_min = 32000,
> +			.rate_max = 192000,
>  			.formats = WM8776_FORMATS,
>  		},
>  		.ops = &wm8776_dac_ops,
> @@ -362,7 +359,9 @@ static struct snd_soc_dai_driver wm8776_dai[] = {
>  			.stream_name = "Capture",
>  			.channels_min = 2,
>  			.channels_max = 2,
> -			.rates = WM8776_RATES,
> +			.rates = SNDRV_PCM_RATE_CONTINUOUS,
> +			.rate_min = 32000,
> +			.rate_max = 96000,
>  			.formats = WM8776_FORMATS,
>  		},
>  		.ops = &wm8776_adc_ops,
> -- 
> 1.7.3.4
> 
> 
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