Re: [alsa-devel] ALSA hw sample rate conversion support

30 Mar 2011


      On Wed, 2011-03-30 at 21:02 +0530, Koul, Vinod wrote:
...
Aisheng Dong wrote:
...
Hi ALL,
Does ALSA core support hw sample rate conversion now?
Our soc has a HW sample rate converter module inside,
I wonder if current ALSA core provide interface to support hw sample
rate conversion?
Assuming the SRC is inside SoC and you are converting sampling rate of stream
and sending at different rate, then I have a patch for you.
Basically the soc side hw_params should call a new API which call
codec_set_params() and sets the matching rate.
Something like this in soc-core
+int snd_soc_codec_set_params(struct snd_soc_codec *codec, unsigned int param)
+{

  if (codec->driver->set_params)


          return codec->driver->set_params(codec, param);


  else


          return -EINVAL;


+}
+EXPORT_SYMBOL_GPL(snd_soc_codec_set_params);
Mark,
Would you okay with such a patch where DSP is doing some conversion and codec
will get different params from what stream is set up? And we make sure 
conversion is synced
Fwiw, I've already implemented a hw_params() fixup between the DSP and
CODEC drivers. This is in my dsp branch atm here :-
http://git.kernel.org/?p=linux/kernel/git/lrg/asoc-2.6.git;a=shortlog;h=refs...
This allows us to rewrite channels, rates, formats etc. depending on the
use case and can be part of the machine driver e.g. (from sdp4430.c)
static int mcbsp_be_hw_params_fixup(struct snd_soc_pcm_runtime *rtd,
    		struct snd_pcm_hw_params *params)
{
    struct snd_interval *channels = hw_param_interval(params,
                                       SNDRV_PCM_HW_PARAM_CHANNELS);
    unsigned int be_id = rtd->dai_link->be_id;
if (be_id == OMAP_ABE_DAI_MM_FM)
    	channels->min = 2;
    else if (be_id == OMAP_ABE_DAI_BT_VX)
    	channels->min = 1;
    snd_mask_set(&params->masks[SNDRV_PCM_HW_PARAM_FORMAT -
                                SNDRV_PCM_HW_PARAM_FIRST_MASK],
                                SNDRV_PCM_FORMAT_S16_LE);
    return 0;
}
static int dmic_be_hw_params_fixup(struct snd_soc_pcm_runtime *rtd,
    		struct snd_pcm_hw_params *params)
{
    struct snd_interval *rate = hw_param_interval(params,
    		SNDRV_PCM_HW_PARAM_RATE);
/* The ABE will covert the FE rate to 96k */
    rate->min = rate->max = 96000;
snd_mask_set(&params->masks[SNDRV_PCM_HW_PARAM_FORMAT -
                                SNDRV_PCM_HW_PARAM_FIRST_MASK],
                                SNDRV_PCM_FORMAT_S32_LE);
    return 0;
}
I intend to start upstreaming all this stuff when I return from holiday
on the 11th April (in time for 2.6.40).
Liam

Re: [alsa-devel] ALSA hw sample rate conversion support

Liam Girdwood