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    SubjectRe: [PATCH AUTOSEL 5.4 057/130] ALSA: usb-audio: Check valid altsetting at parsing rates for UAC2/3
    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@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@motu.com>
    >> Tested-by: Keith Milner <kamilner@superlative.org>
    >> Tested-by: Dylan Robinson <dylan_robinson@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@suse.de>
    >> Signed-off-by: Sasha Levin <sashal@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

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