Messages in this thread Patch in this message | | | Date | Thu, 21 Feb 2013 10:03:34 +0100 | From | Takashi Iwai <> | Subject | Re: [PATCH] ALSA: usb: Fix Processing Unit Descriptor parsers |
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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
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