[alsa-devel] [RFC PATCH 2/3] ALSA:core: Add rate 24kHz

[Pierre-Louis Bossart]

On 9/5/19 12:48 AM, Takashi Iwai wrote:
> On Thu, 05 Sep 2019 07:33:00 +0200,
> Pawel Harlozinski wrote:
>>
>> Adds SNDRV_PCM_RATE_24000 at the bottom to keep backward compability
>> with alsa library.
>>
>> Signed-off-by: Pawel Harlozinski <pawel.harlozinski at linux.intel.com>
> 
> No.  Such a fancy rate has to be handled inside the driver locally
> instead of adding to the common rate.

It's not that crazy, this is supported in the HDaudio spec:

Sample Base Rate Divisor (DIV):
000 = Divide by 1 (48 kHz, 44.1 kHz)
001 = Divide by 2 (24 kHz, 22.05 kHz)

I am not sure why 22.05 made the cut and not 24 kHz, they are both 
derived from common clocks with the same divider... Same for 11.025 and 
12...

> 
> 
> Takashi
> 
>> ---
>>   include/sound/pcm.h     | 1 +
>>   sound/core/pcm_native.c | 4 ++--
>>   2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/sound/pcm.h b/include/sound/pcm.h
>> index bbe6eb1ff5d2..09d0a2a2dce8 100644
>> --- a/include/sound/pcm.h
>> +++ b/include/sound/pcm.h
>> @@ -119,6 +119,7 @@ struct snd_pcm_ops {
>>   #define SNDRV_PCM_RATE_192000		(1<<12)		/* 192000Hz */
>>   #define SNDRV_PCM_RATE_352800		(1<<13)		/* 352800Hz */
>>   #define SNDRV_PCM_RATE_384000		(1<<14)		/* 384000Hz */
>> +#define SNDRV_PCM_RATE_24000		(1<<15)		/* 24000Hz */
>>   
>>   #define SNDRV_PCM_RATE_CONTINUOUS	(1<<30)		/* continuous range */
>>   #define SNDRV_PCM_RATE_KNOT		(1<<31)		/* supports more non-continuos rates */
>> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
>> index 11e653c8aa0e..f52f28e3edb1 100644
>> --- a/sound/core/pcm_native.c
>> +++ b/sound/core/pcm_native.c
>> @@ -2164,13 +2164,13 @@ static int snd_pcm_hw_rule_sample_bits(struct snd_pcm_hw_params *params,
>>   	return snd_interval_refine(hw_param_interval(params, rule->var), &t);
>>   }
>>   
>> -#if SNDRV_PCM_RATE_5512 != 1 << 0 || SNDRV_PCM_RATE_192000 != 1 << 12
>> +#if SNDRV_PCM_RATE_5512 != 1 << 0 || SNDRV_PCM_RATE_192000 != 1 << 12 ||  SNDRV_PCM_RATE_24000 != 1 << 15
>>   #error "Change this table"
>>   #endif
>>   
>>   static const unsigned int rates[] = {
>>   	5512, 8000, 11025, 16000, 22050, 32000, 44100,
>> -	48000, 64000, 88200, 96000, 176400, 192000, 352800, 384000
>> +	48000, 64000, 88200, 96000, 176400, 192000, 352800, 384000, 24000
>>   };
>>   
>>   const struct snd_pcm_hw_constraint_list snd_pcm_known_rates = {
>> -- 
>> 2.17.1
>>