[PATCH] ALSA: usb-audio: Fix microphone sound on HD webcam.

[wangdicheng <wangdich9700@163.com>]

From: wangdicheng <wangdicheng@kylinos.cn>

I own an external usb Webcam, HD webcam, which had low mic volume and
inconsistent sound quality. Video works as expected.

(snip)
[   95.473820][ 1] [   T73] usb 5-2.2: new high-speed USB device number 7 using xhci_hcd
[   95.773974][ 1] [   T73] usb 5-2.2: New USB device found, idVendor=1bcf, idProduct=2281, bcdDevice= 0.05
[   95.783445][ 1] [   T73] usb 5-2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[   95.791872][ 1] [   T73] usb 5-2.2: Product: HD webcam
[   95.797001][ 1] [   T73] usb 5-2.2: Manufacturer: Sunplus IT Co
[   95.802996][ 1] [   T73] usb 5-2.2: SerialNumber: 20200513
[   96.092610][ 2] [ T3680] usb 5-2.2: Warning! Unlikely big volume range (=4096), cval->res is probably wrong.
[   96.102436][ 2] [ T3680] usb 5-2.2: [5] FU [Mic Capture Volume] ch = 1, val = 0/4096/1

Set up quirk cval->res to 16 for 256 levels,
Set GET_SAMPLE_RATE quirk flag to stop trying to get the sample rate.
Confirmed that happened anyway later due to the backoff mechanism,
After 3 failures.

All audio stream on device interfaces share the same values,
apart from wMaxPacketSize and tSamFreq :

      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        3
      bAlternateSetting       4
      bNumEndpoints           1
      bInterfaceClass         1 Audio

Interface Descriptor:
  bLength                 9
  bDescriptorType         4
  bInterfaceNumber        3
  bAlternateSetting       4
  bNumEndpoints           1
  bInterfaceClass         1 Audio
  bInterfaceSubClass      2 Streaming
  bInterfaceProtocol      0
  iInterface              0
  AudioStreaming Interface Descriptor:
    bLength                 7
    bDescriptorType        36
    bDescriptorSubtype      1 (AS_GENERAL)
    bTerminalLink           3
    bDelay                  1 frames
    wFormatTag         0x0001 PCM
  AudioStreaming Interface Descriptor:
    bLength                11
    bDescriptorType        36
    bDescriptorSubtype      2 (FORMAT_TYPE)
    bFormatType             1 (FORMAT_TYPE_I)
    bNrChannels             1
    bSubframeSize           2
    bBitResolution         16
    bSamFreqType            1 Discrete
    tSamFreq[ 0]        48000
  Endpoint Descriptor:
    bLength                 9
    bDescriptorType         5
    bEndpointAddress     0x86  EP 6 IN
    bmAttributes            5
      Transfer Type            Isochronous
      Synch Type               Asynchronous
      Usage Type               Data
    wMaxPacketSize     0x0064  1x 100 bytes
    bInterval               4
    bRefresh                0
    bSynchAddress           0
    AudioStreaming Endpoint Descriptor:
      bLength                 7
      bDescriptorType        37
      bDescriptorSubtype      1 (EP_GENERAL)
      bmAttributes         0x01
        Sampling Frequency
      bLockDelayUnits         0 Undefined
      wLockDelay         0x0000
(snip)

Testing patch provides consistent good sound recording quality and volume range.

(snip)
[   95.473820][ 1] [   T73] usb 5-2.2: new high-speed USB device number 7 using xhci_hcd
[   95.773974][ 1] [   T73] usb 5-2.2: New USB device found, idVendor=1bcf, idProduct=2281, bcdDevice= 0.05
[   95.783445][ 1] [   T73] usb 5-2.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[   95.791872][ 1] [   T73] usb 5-2.2: Product: HD webcam
[   95.797001][ 1] [   T73] usb 5-2.2: Manufacturer: Sunplus IT Co
[   95.802996][ 1] [   T73] usb 5-2.2: SerialNumber: 20200513
[   96.110630][ 3] [ T3680] usbcore: registered new interface driver snd-usb-audio
[   96.114329][ 7] [ T3677] usb 5-2.2: Found UVC 1.00 device HD webcam (1bcf:2281)
[   96.167555][ 7] [ T3677] usbcore: registered new interface driver uvcvideo

Signed-off-by: wangdicheng <wangdicheng@kylinos.cn>
---
 sound/usb/mixer.c  | 7 +++++++
 sound/usb/quirks.c | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 409fc1164694..561c974a4f14 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1211,6 +1211,13 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 			cval->res = 16;
 		}
 		break;
+	case USB_ID(0x1bcf, 0x2281): /* FHD Webcam */
+		if (!strcmp(kctl->id.name, "Mic Capture Volume")) {
+			usb_audio_info(chip,
+				"set resolution quirk: cval->res = 16\n");
+			cval->res = 16;
+		}
+		break;
 	}
 }
 
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 4e64842245e1..16070cd7440e 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -2179,6 +2179,8 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = {
 		   QUIRK_FLAG_FIXED_RATE),
 	DEVICE_FLG(0x1bcf, 0x2283, /* NexiGo N930AF FHD Webcam */
 		   QUIRK_FLAG_GET_SAMPLE_RATE),
+	DEVICE_FLG(0x1bcf, 0x2281, /* FHD Webcam */
+			QUIRK_FLAG_GET_SAMPLE_RATE),
 
 	/* Vendor matches */
 	VENDOR_FLG(0x045e, /* MS Lifecam */
-- 
2.25.1