[ 26/53] ALSA: usb: Fix Processing Unit Descriptor parsers

Greg Kroah-Hartman
2013-02-26T23:59:07Z

From: Pawel Moll <mail@pawelmoll.com>

commit b531f81b0d70ffbe8d70500512483227cc532608 upstream.

Commit 99fc86450c439039d2ef88d06b222fd51a779176 "ALSA: usb-mixer:
parse descriptors with structs" introduced a set of useful parsers
for descriptors. Unfortunately the parses for the Processing Unit
Descriptor came with a very subtle bug...

Functions uac_processing_unit_iProcessing() and
uac_processing_unit_specific() were indexing the baSourceID array
forgetting the fields before the iProcessing and process-specific
descriptors.

The problem was observed with Sound Blaster Extigy mixer,
where nNrModes in Up/Down-mix Processing Unit Descriptor
was accessed at offset 10 of the descriptor (value 0)
instead of offset 15 (value 7). In result the resulting
control had interesting limit values:

Simple mixer control 'Channel Routing Mode Select',0
Capabilities: volume volume-joined penum
Playback channels: Mono
Capture channels: Mono
Limits: 0 - -1
Mono: -1 [100%]

Fixed by starting from the bmControls, which was calculated
correctly, instead of baSourceID.

Now the mentioned control is fine:

Simple mixer control 'Channel Routing Mode Select',0
Capabilities: volume volume-joined penum
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 6
Mono: 0 [0%]

Signed-off-by: Pawel Moll <mail@pawelmoll.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/usb/audio.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/include/linux/usb/audio.h
+++ b/include/linux/usb/audio.h
@@ -384,14 +384,16 @@ static inline __u8 uac_processing_unit_i
int protocol)
{
__u8 control_size = uac_processing_unit_bControlSize(desc, protocol);
- return desc->baSourceID[desc->bNrInPins + control_size];
+ return *(uac_processing_unit_bmControls(desc, protocol)
+ + control_size);
}

static inline __u8 *uac_processing_unit_specific(struct uac_processing_unit_descriptor *desc,
int protocol)
{
__u8 control_size = uac_processing_unit_bControlSize(desc, protocol);
- return &desc->baSourceID[desc->bNrInPins + control_size + 1];
+ return uac_processing_unit_bmControls(desc, protocol)
+ + control_size + 1;
}

/* 4.5.2 Class-Specific AS Interface Descriptor */