ALSA: usb-audio: Add GET_SAMPLE_RATE quirk for C-Media CM6206

The C-Media CM6206 (0d8c:0102) truncates the three-byte sample rate it
returns for UAC_GET_CUR to its two low bytes.  After the rate has been
set to 96000 (0x017700) the device reports back 30464 (0x007700).

At probe time the driver initializes every altsetting to its maximum
rate, so altsetting 5 is set to 96000 and the warning appears on each
plug-in, before anything has opened the device:

  usb 3-1.3: 1:5 Set sample rate 96000, clock 0
  usb 3-1.3: current rate 30464 is different from the runtime rate 96000

That altsetting is the one parse_audio_format_rates_v1() already fixes
up for this chip, so this affects every CM6206.

Only the read-back is broken, the rate itself is applied: a 1 kHz sine
rendered at 96 kHz is recovered at 1000.2 Hz, and a silent fallback to
48000 would have been reported as 0x00bb80 rather than as the low half
of the requested rate.

Add a QUIRK_FLAG_GET_SAMPLE_RATE entry for the device so the read-back
is skipped.  Setting the same flag through the quirk_flags module
parameter makes the warning disappear while the 96000 init still
happens.

Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Link: https://patch.msgid.link/20260728222239.62749-1-mikhail.v.gavrilov@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 40aa40fccb46f4e82d4d47700d83b94b56cf13c6..d2a111ee50ab92374e46dbec5b6c8f1d90dd7fd7 100644 (file)
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2347,6 +2347,8 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
                   QUIRK_FLAG_MIXER_PLAYBACK_MIN_MUTE),
        DEVICE_FLG(0x0d8c, 0x0014, /* C-Media */
                   QUIRK_FLAG_CTL_MSG_DELAY_1M | QUIRK_FLAG_MIXER_PLAYBACK_MIN_MUTE),
+       DEVICE_FLG(0x0d8c, 0x0102, /* C-Media CM6206 */
+                  QUIRK_FLAG_GET_SAMPLE_RATE),
        DEVICE_FLG(0x0e0b, 0xfa01, /* Feaulle Rainbow */
                   QUIRK_FLAG_GET_SAMPLE_RATE | QUIRK_FLAG_MIXER_PLAYBACK_MIN_MUTE),
        DEVICE_FLG(0x0ecb, 0x205c, /* JBL Quantum610 Wireless */