[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>

1 files changed, 46 insertions, 0 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 087f9b64d8a0..664dd4c21e66 100644
--- 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;