[alsa-devel] [PATCH] sound/usb: add dB range mapping quirks.

[Yao-Wen Mao]

Some usb audio devices don't follow the specification of the
volume range. Add dB_mapping_quirks to fix some devices' dB
ranges so that the function snd_mixer_selem_set_playback_dB in
alsa-lib can set the correct value for those devices.

Signed-off-by: Yao-Wen Mao <yaowen at google.com>
---
 sound/usb/mixer.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 6b3acba..b6b27dc 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -933,6 +933,32 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 	}
 }
 
+/* dB mapping quirks */
+static void dB_mapping_quirks(struct usb_mixer_elem_info *cval,
+			      struct snd_kcontrol *kctl)
+{
+	switch (cval->mixer->chip->usb_id) {
+	case USB_ID(0x05a7, 0x1020): /* Bose Companion 5 */
+		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
+			cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 16;
+			cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 16;
+		}
+		break;
+	case USB_ID(0x21b4, 0x0081): /* Dragonfly DAC 1.2 */
+		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
+			cval->dBmin = convert_signed_value(cval, cval->min) * 100;
+			cval->dBmax = convert_signed_value(cval, cval->max) * 100;
+		}
+		break;
+	case USB_ID(0x046d, 0x0a29): /* Logitech H800 */
+		if (strcmp(kctl->id.name, "PCM Playback Volume") == 0) {
+			cval->dBmin = convert_signed_value(cval, cval->min);
+			cval->dBmax = convert_signed_value(cval, cval->max);
+		}
+		break;
+	}
+}
+
 /*
  * retrieve the minimum and maximum values for the specified control
  */
@@ -1027,6 +1053,10 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
 	 */
 	cval->dBmin = (convert_signed_value(cval, cval->min) * 100) / 256;
 	cval->dBmax = (convert_signed_value(cval, cval->max) * 100) / 256;
+
+	if (kctl)
+		dB_mapping_quirks(cval, kctl);
+
 	if (cval->dBmin > cval->dBmax) {
 		/* something is wrong; assume it's either from/to 0dB */
 		if (cval->dBmin < 0)
-- 
2.5.0.rc2.392.g76e840b