[alsa-devel] [PATCH 4/4] ALSA: usb-audio: fix UAC2 control value queries

[Daniel Mack]

UAC2 controls can be queried in 1-byte, 2-byte or 4-byte request blocks.
The size is actually determined by the number of bytes requested, and as
everything is little-endian, we can always go for the 4-byte variant.

Also, the MIN, MAX and RES value computations were using a wrong offset.

Signed-off-by: Daniel Mack <daniel at caiaq.de>
Reported-by: Alex Lee <alexlee188 at gmail.com>
---
 sound/usb/mixer.c |   19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index a060d00..6939d0f 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -297,20 +297,27 @@ static int get_ctl_value_v1(struct usb_mixer_elem_info *cval, int request, int v
 
 static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request, int validx, int *value_ret)
 {
-	unsigned char buf[14]; /* enough space for one range of 4 bytes */
+	unsigned char buf[2 + 3*sizeof(__u16)]; /* enough space for one range */
 	unsigned char *val;
-	int ret;
+	int ret, size;
 	__u8 bRequest;
 
-	bRequest = (request == UAC_GET_CUR) ?
-		UAC2_CS_CUR : UAC2_CS_RANGE;
+	if (request == UAC_GET_CUR) {
+		bRequest = UAC2_CS_CUR;
+		size = sizeof(__u16);
+	} else {
+		bRequest = UAC2_CS_RANGE;
+		size = sizeof(buf);
+	}
+
+	memset(buf, 0, sizeof(buf));
 
 	ret = snd_usb_ctl_msg(cval->mixer->chip->dev,
 			      usb_rcvctrlpipe(cval->mixer->chip->dev, 0),
 			      bRequest,
 			      USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
 			      validx, cval->mixer->ctrlif | (cval->id << 8),
-			      buf, sizeof(buf), 1000);
+			      buf, size, 1000);
 
 	if (ret < 0) {
 		snd_printk(KERN_ERR "cannot get ctl value: req = %#x, wValue = %#x, wIndex = %#x, type = %d\n",
@@ -318,6 +325,8 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request, int v
 		return ret;
 	}
 
+	/* FIXME: how should we handle multiple triplets here? */
+
 	switch (request) {
 	case UAC_GET_CUR:
 		val = buf;
-- 
1.7.1