[PATCH 5.6 108/167] ALSA: usb-audio: Filter out unsupported sample rates on Focusrite devices

From: Greg Kroah-Hartman
Date: Tue Apr 28 2020 - 14:35:07 EST


From: Alexander Tsoy <alexander@xxxxxxx>

commit 1c826792586f526a5a5cd21d55aad388f5bb0b23 upstream.

Many Focusrite devices supports a limited set of sample rates per
altsetting. These includes audio interfaces with ADAT ports:
- Scarlett 18i6, 18i8 1st gen, 18i20 1st gen;
- Scarlett 18i8 2nd gen, 18i20 2nd gen;
- Scarlett 18i8 3rd gen, 18i20 3rd gen;
- Clarett 2Pre USB, 4Pre USB, 8Pre USB.

Maximum rate is exposed in the last 4 bytes of Format Type descriptor
which has a non-standard bLength = 10.

Tested-by: Alexey Skobkin <skobkin-ru@xxxxx>
Signed-off-by: Alexander Tsoy <alexander@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200418175815.12211-1-alexander@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
sound/usb/format.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)

--- a/sound/usb/format.c
+++ b/sound/usb/format.c
@@ -248,6 +248,52 @@ static int parse_audio_format_rates_v1(s
}

/*
+ * Many Focusrite devices supports a limited set of sampling rates per
+ * altsetting. Maximum rate is exposed in the last 4 bytes of Format Type
+ * descriptor which has a non-standard bLength = 10.
+ */
+static bool focusrite_valid_sample_rate(struct snd_usb_audio *chip,
+ struct audioformat *fp,
+ unsigned int rate)
+{
+ struct usb_interface *iface;
+ struct usb_host_interface *alts;
+ unsigned char *fmt;
+ unsigned int max_rate;
+
+ iface = usb_ifnum_to_if(chip->dev, fp->iface);
+ if (!iface)
+ return true;
+
+ alts = &iface->altsetting[fp->altset_idx];
+ fmt = snd_usb_find_csint_desc(alts->extra, alts->extralen,
+ NULL, UAC_FORMAT_TYPE);
+ if (!fmt)
+ return true;
+
+ if (fmt[0] == 10) { /* bLength */
+ max_rate = combine_quad(&fmt[6]);
+
+ /* Validate max rate */
+ if (max_rate != 48000 &&
+ max_rate != 96000 &&
+ max_rate != 192000 &&
+ max_rate != 384000) {
+
+ usb_audio_info(chip,
+ "%u:%d : unexpected max rate: %u\n",
+ fp->iface, fp->altsetting, max_rate);
+
+ return true;
+ }
+
+ return rate <= max_rate;
+ }
+
+ return true;
+}
+
+/*
* Helper function to walk the array of sample rate triplets reported by
* the device. The problem is that we need to parse whole array first to
* get to know how many sample rates we have to expect.
@@ -283,6 +329,11 @@ static int parse_uac2_sample_rate_range(
}

for (rate = min; rate <= max; rate += res) {
+ /* Filter out invalid rates on Focusrite devices */
+ if (USB_ID_VENDOR(chip->usb_id) == 0x1235 &&
+ !focusrite_valid_sample_rate(chip, fp, rate))
+ goto skip_rate;
+
if (fp->rate_table)
fp->rate_table[nr_rates] = rate;
if (!fp->rate_min || rate < fp->rate_min)
@@ -297,6 +348,7 @@ static int parse_uac2_sample_rate_range(
break;
}

+skip_rate:
/* avoid endless loop */
if (res == 0)
break;