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Commit a79eee8d authored by Luke Ross's avatar Luke Ross Committed by Jaroslav Kysela
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[ALSA] Support for non-standard rates in USB audio driver 



There's at least one USB audio chipset out there which supports only one
non-standard rate (ID 0e6a:0310 supports 46875Hz). There's a few other
patches for this card which are unsatisfactory because they attempt to
map this rate to 44.1k leading to sound distortion.
The patch below uses SNDRV_PCM_RATE_KNOT to properly support the
non-standard rates where they are available.

Signed-off-by: default avatarLuke Ross <luke@lukeross.name>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarJaroslav Kysela <perex@suse.cz>
parent 9f458e7f

sound/usb/usbaudio.c

+46 −0
Original line number Diff line number Diff line
@@ -123,6 +123,7 @@ struct audioformat { 
	unsigned int rate_min, rate_max;	/* min/max rates */

	unsigned int nr_rates;		/* number of rate table entries */

	unsigned int *rate_table;	/* rate table */

	unsigned int needs_knot;	/* any unusual rates? */

};



struct snd_usb_substream;
@@ -1759,6 +1760,9 @@ static int check_hw_params_convention(struct snd_usb_substream *subs) 
		}

		channels[f->format] |= (1 << f->channels);

		rates[f->format] |= f->rates;

		/* needs knot? */

		if (f->needs_knot)

			goto __out;

	}

	/* check whether channels and rates match for all formats */

	cmaster = rmaster = 0;
@@ -1799,6 +1803,38 @@ static int check_hw_params_convention(struct snd_usb_substream *subs) 
	return err;

}



/*

 *  If the device supports unusual bit rates, does the request meet these?

 */

static int snd_usb_pcm_check_knot(struct snd_pcm_runtime *runtime,

				  struct snd_usb_substream *subs)

{

	struct list_head *p;

	struct snd_pcm_hw_constraint_list constraints_rates;

	int err;



	list_for_each(p, &subs->fmt_list) {

		struct audioformat *fp;

		fp = list_entry(p, struct audioformat, list);



		if (!fp->needs_knot)

			continue;



		constraints_rates.count = fp->nr_rates;

		constraints_rates.list = fp->rate_table;

		constraints_rates.mask = 0;



		err = snd_pcm_hw_constraint_list(runtime, 0,

			SNDRV_PCM_HW_PARAM_RATE,

			&constraints_rates);



		if (err < 0)

			return err;

	}



	return 0;

}





/*

 * set up the runtime hardware information.
@@ -1861,6 +1897,8 @@ static int setup_hw_info(struct snd_pcm_runtime *runtime, struct snd_usb_substre 
					       SNDRV_PCM_HW_PARAM_CHANNELS,

					       -1)) < 0)

			return err;

		if ((err = snd_usb_pcm_check_knot(runtime, subs)) < 0)

			return err;

	}

	return 0;

}
@@ -2406,6 +2444,7 @@ static int parse_audio_format_rates(struct snd_usb_audio *chip, struct audioform 
				    unsigned char *fmt, int offset)

{

	int nr_rates = fmt[offset];

	int found;

	if (fmt[0] < offset + 1 + 3 * (nr_rates ? nr_rates : 2)) {

		snd_printk(KERN_ERR "%d:%u:%d : invalid FORMAT_TYPE desc\n",

				   chip->dev->devnum, fp->iface, fp->altsetting);
@@ -2428,6 +2467,7 @@ static int parse_audio_format_rates(struct snd_usb_audio *chip, struct audioform 
			return -1;

		}



		fp->needs_knot = 0;

		fp->nr_rates = nr_rates;

		fp->rate_min = fp->rate_max = combine_triple(&fmt[8]);

		for (r = 0, idx = offset + 1; r < nr_rates; r++, idx += 3) {
@@ -2436,13 +2476,19 @@ static int parse_audio_format_rates(struct snd_usb_audio *chip, struct audioform 
				fp->rate_min = rate;

			else if (rate > fp->rate_max)

				fp->rate_max = rate;

			found = 0;

			for (c = 0; c < (int)ARRAY_SIZE(conv_rates); c++) {

				if (rate == conv_rates[c]) {

					found = 1;

					fp->rates |= (1 << c);

					break;

				}

			}

			if (!found)

				fp->needs_knot = 1;

		}

		if (fp->needs_knot)

			fp->rates |= SNDRV_PCM_RATE_KNOT;

	} else {

		/* continuous rates */

		fp->rates = SNDRV_PCM_RATE_CONTINUOUS;