[PATCH AUTOSEL 5.4 057/130] ALSA: usb-audio: Check valid altsetting at parsing rates for UAC2/3

[Sasha Levin]

On Wed, Dec 23, 2020 at 08:09:41AM +0100, Takashi Iwai wrote:
>On Wed, 23 Dec 2020 03:17:00 +0100,
>Sasha Levin wrote:
>>
>> From: Takashi Iwai <tiwai at suse.de>
>>
>> [ Upstream commit 93db51d06b32227319dae2ac289029ccf1b33181 ]
>>
>> The current driver code assumes blindly that all found sample rates for
>> the same endpoint from the UAC2 and UAC3 descriptors can be used no
>> matter which altsetting, but actually this was wrong: some devices
>> accept only limited sample rates in each altsetting.  For determining
>> which altsetting supports which rate, we need to verify each sample rate
>> and check the validity via UAC2_AS_VAL_ALT_SETTINGS.  This control
>> reports back the available altsettings as a bitmap.
>>
>> This patch implements the missing piece above, the verification and
>> reconstructs the sample rate tables based on the result.
>>
>> An open question is how to deal with the altsettings that ended up
>> with no valid sample rates after verification.  At least, there is a
>> device that showed this problem although the sample rates did work in
>> the later usage (see bug link).  For now, we accept such an altset as
>> is, assuming that it's a firmware bug.
>>
>> Reported-by: Dylan Robinson <dylan_robinson at motu.com>
>> Tested-by: Keith Milner <kamilner at superlative.org>
>> Tested-by: Dylan Robinson <dylan_robinson at motu.com>
>> BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1178203
>> Link: https://lore.kernel.org/r/20201123085347.19667-4-tiwai@suse.de
>> Signed-off-by: Takashi Iwai <tiwai at suse.de>
>> Signed-off-by: Sasha Levin <sashal at kernel.org>
>
>Please drop this for 5.4 or older.  At least this caused some problem
>on 5.3 kernel that confused USB core by some reason while it works
>fine with the recent upstream.

Will do, thanks.

-- 
Thanks,
Sasha