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From:   Alexey Brodkin <Alexey.Brodkin@synopsys.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     linux-stable <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Corentin Labbe <clabbe@baylibre.com>,
        "khilman@baylibre.com" <khilman@baylibre.com>,
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        <linux-snps-arc@lists.infradead.org>,
        Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>,
        Vineet Gupta <Vineet.Gupta1@synopsys.com>
Subject: RE: [PATCH v2 2/2] ARC: enable uboot support unconditionally
Thread-Topic: [PATCH v2 2/2] ARC: enable uboot support unconditionally
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Date:   Fri, 2 Aug 2019 16:25:39 +0000
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Hi Greg,

> > May we have this one back-ported to linux-4.19.y?
> >
> > It was initially applied to Linus' tree during 5.0 development
> > cycle [1] but was never back-ported.
> >
> > Now w/o that patch in KernelCI we see boot failure on ARC HSDK
> > board [2] as opposed to normally working later kernel versions.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/=
commit/?id=3D493a2f812446e92bcb1e69a77381b4d39808d730
> > [2] https://storage.kernelci.org/stable/linux-4.19.y/v4.19.59/arc/hsdk_=
defconfig/gcc-8/lab-baylibre/boot-hsdk.txt
> >
> > Below is that same patch but rebased on linux-4.19 as in its pristine
> > form it won't apply due to offset of one of hunks.
>=20
> Why is this patch ok for stable kernel trees?  Are you not removing
> existing support in 4.19 for a feature that people might be using there?
> What bug is this fixing that requires this removal?

This patch removes a Kconfig option in a trade for properly working
detection of arguments passed from U-Boot.

Back in the day [3] we had to add that option to get kernel reliably workin=
g
in use-cases w/o U-Boot (those were typically loading kernel image via JTAG=
).
But with a couple of fixes applied to linux-4.19.y already we no longer nee=
d
that explicit toggle as we may rely on data passed via dedicated registers
and thus automatically know if there was U-Boot which passed some info to
the kernel or there was no U-Boot and we don't need to mess with garbage in
those registers.

Main reason is to make vanilla 4.19.y kernels usable on HSDK board in Kerne=
lCI
environment. Now they don't boot, see [2] as in HSDK's defconfig ARC_UBOOT_=
SUPPORT
is not set. So we have 2 solutions:

1. Add ARC_UBOOT_SUPPORT to arch/arc/configs/hsdk_defconfig
   But we cannot do it for vanilla kernel because we simply cannot even sub=
mit that
   change to the Linus' tree as that Kconfig option was removed.
   Which means we cannot back-port it, right :)

2. Back-port proposed patch which already exists in the Linus'tree and thus=
 is
   perfectly back-portable.

Makes sense?

-Alexey

[2] https://storage.kernelci.org/stable/linux-4.19.y/v4.19.59/arc/hsdk_defc=
onfig/gcc-8/lab-baylibre/boot-hsdk.txt
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/comm=
it/?id=3D036b2c5664281e7da5a89c9f742491f30966485f