[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: Luke Ross <luke@lukeross.name>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 087f9b6..664dd4c 100644 (file)
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -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;