Re: [PATCH AUTOSEL 3.18 04/98] USB: qcserial: Fix support for HP lt4112 LTE/HSPA+ Gobi 4G Modem

Sasha Levin
2018-10-26T19:35:56Z

On Fri, Oct 26, 2018 at 10:49:20AM +0200, Johan Hovold wrote:
>On Thu, Oct 25, 2018 at 10:17:19AM -0400, Sasha Levin wrote:
>> From: Bjï¿½rn Mork <bjorn@mork.no>
>>
>> [ Upstream commit 59536da34513c594af2a6fd35ba65ea45b6960a1 ]
>>
>> The DEVICE_HWI type was added under the faulty assumption that Huawei
>> devices based on Qualcomm chipsets and firmware use the static USB
>> interface numbering known from Gobi devices. But this model does
>> not apply to Huawei devices like the HP branded lt4112 (Huawei me906e).
>> Huawei firmwares will dynamically assign interface numbers. Functions
>> are renumbered when the firmware is reconfigured.
>>
>> Fix by changing the DEVICE_HWI type to use a simplified version
>> of Huawei's subclass + protocol scheme: Blacklisting known network
>> interface combinations and assuming the rest are serial.
>>
>> Reported-and-tested-by: Muri Nicanor <muri+libqmi@immerda.ch>
>> Tested-by: Martin Hauke <mardnh@gmx.de>
>> Cc: <stable@vger.kernel.org>
>> Fixes: e7181d005e84 ("USB: qcserial: Add support for HP lt4112 LTE/HSPA+ Gobi 4G Modem")
>> Signed-off-by: Bjï¿½rn Mork <bjorn@mork.no>
>> Signed-off-by: Johan Hovold <johan@kernel.org>
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>
>This one is interesting though; it was marked for stable and has a
>proper fixes tag for a commit that went into 4.19. That patch in turn
>had a stable tag (new device id type patch) and was backported also to
>other active stable trees at the time.
>
>Guess the stable maintainers need to check if the offending patch has
>already been backported when determining how far back to apply a follow
>up fix.
>
>Note that the stable tag above lacks a version comment (e.g. "# 4.19"),
>but I can see how that may be too subtle to convey this (and not all
>maintainers use those). Perhaps an explicit comment should just be added
>in such cases.

Right, the whole "fix for a fix" issue is what this patch series tries
to address (you'll notice that *most* commits follow this pattern).

I'm not sure why Greg's tools missed it to begin with, but hopefully
this patch series will catch up with that.

--
Thanks,
Sasha