On 21.02.2013 10:03, Takashi Iwai wrote:
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?
Looks good to me too. and this should be marked for stable of course.
Thanks for fixing this, Pawell!
Daniel