linux-kernel - Re: [PATCH] ALSA: usb: Fix Processing Unit Descriptor parsers

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Date:	Thu, 21 Feb 2013 14:20:19 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Daniel Mack <zonque@...il.com>
Cc:	Pawel Moll <mail@...elmoll.com>, Jaroslav Kysela <perex@...ex.cz>,
	Daniel Mack <daniel@...aq.de>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: usb: Fix Processing Unit Descriptor parsers

At Thu, 21 Feb 2013 13:10:16 +0100,
Daniel Mack wrote:
> 
> 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@...elmoll.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!

OK, applied now.  Thanks.


Takashi
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