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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Pali =?utf-8?Q?Roh=C3=A1r?= <pali@kernel.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Regression: Linux v5.15+ does not boot on Freescale P2020
In-Reply-To: <20220723150702.jecerkhxhy65dgww@pali>
References: <20220722090929.mwhmxxdd7yioxqpz@pali>
 <6b227478-73b8-2a97-1c78-89570d928739@csgroup.eu>
 <20220723150702.jecerkhxhy65dgww@pali>
Date:   Mon, 25 Jul 2022 18:20:01 +1000
Message-ID: <875yjld2oe.fsf@mpe.ellerman.id.au>
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Pali Roh=C3=A1r <pali@kernel.org> writes:
> On Saturday 23 July 2022 14:42:22 Christophe Leroy wrote:
>> Le 22/07/2022 =C3=A0 11:09, Pali Roh=C3=A1r a =C3=A9crit=C2=A0:
>> > Trying to boot mainline Linux kernel v5.15+, including current version
>> > from master branch, on Freescale P2020 does not work. Kernel does not
>> > print anything to serial console, seems that it does not work and after
>> > timeout watchdog reset the board.
>>=20
>> Can you provide more information ? Which defconfig or .config, which=20
>> version of gcc, etc ... ?
>
> I used default defconfig for mpc85xx with gcc 8, compilation for e500
> cores.
>
> If you need exact .config content I can send it during week.
>
>> > I run git bisect and it found following commit:
>> >=20
>> > 9401f4e46cf6965e23738f70e149172344a01eef is the first bad commit
>> > commit 9401f4e46cf6965e23738f70e149172344a01eef
>> > Author: Christophe Leroy <christophe.leroy@csgroup.eu>
>> > Date:   Tue Mar 2 08:48:11 2021 +0000
>> >=20
>> >      powerpc: Use lwarx/ldarx directly instead of PPC_LWARX/LDARX macr=
os
>> >=20
>> >      Force the eh flag at 0 on PPC32.
>> >=20
>> >      Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> >      Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>> >      Link: https://lore.kernel.org/r/1fc81f07cabebb875b963e295408cc3dd=
38c8d85.1614674882.git.christophe.leroy@csgroup.eu
>> >=20
>> > :040000 040000 fe6747e45736dfcba74914a9445e5f70f5120600 96358d08b65d32=
00928a973efb5b969b3d45f2b0 M      arch
>> >=20
>> >=20
>> > If I revert this commit then kernel boots correctly. It also boots fine
>> > if I revert this commit on top of master branch.
>> >=20
>> > Freescale P2020 has two 32-bit e500 powerpc cores.
>> >=20
>> > Any idea why above commit is causing crash of the kernel? And why it is
>> > needed? Could eh flag set to 0 cause deadlock?
>>=20
>> Setting the eh flag to 0 is not supposed to be a change introduced by=20
>> that commit. Indeed that commit is not supposed to change anything at=20
>> all in the generated code.
>
> My understanding of that commit is that it changed eh flag parameter
> from 1 to 0 for 32-bit powerpc, including also p2020.

Can you compare the disassembly before and after and find a place where
an instruction has changed?

cheers