At Thu, 21 Feb 2013 01:55:50 +0000, Pawel Moll wrote:
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
include/uapi/linux/usb/audio.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/usb/audio.h b/include/uapi/linux/usb/audio.h index ac90037..d2314be 100644 --- a/include/uapi/linux/usb/audio.h +++ b/include/uapi/linux/usb/audio.h @@ -384,14 +384,16 @@ static inline __u8 uac_processing_unit_iProcessing(struct uac_processing_unit_de 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;}
Looks good to me.
An alternative would be to change uac_processing_unit_bControlSize() to correct the header size, but I don't think it's good, as bControlSize fields in other units show the value including the header size.
Daniel, what do you think?
thanks,
Takashi