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

[Sasha Levin]

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: Bjørn Mork <bjorn@xxxxxxx>
> >
> > [ 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@xxxxxxxxxx>
> > Tested-by: Martin Hauke <mardnh@xxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Fixes: e7181d005e84 ("USB: qcserial: Add support for HP lt4112 LTE/HSPA+ Gobi 4G Modem")
> > Signed-off-by: Bjørn Mork <bjorn@xxxxxxx>
> > Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> 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