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Subject: Re: [PATCH 1/3] MIPS: Introduce WAR_4KC_LLSC config option
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
In-Reply-To: <alpine.DEB.2.21.2305192342180.27887@angie.orcam.me.uk>
Date:   Mon, 22 May 2023 21:46:07 +0100
Cc:     "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        linux-kernel@vger.kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>
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Message-Id: <CB4BAB41-0BE0-4897-AE1E-9A98A6851FEF@flygoat.com>
References: <20230519164753.72065-1-jiaxun.yang@flygoat.com>
 <20230519164753.72065-2-jiaxun.yang@flygoat.com>
 <alpine.DEB.2.21.2305192117230.50034@angie.orcam.me.uk>
 <53043C18-7C75-4D5F-A15E-86D981D19CA8@flygoat.com>
 <alpine.DEB.2.21.2305192342180.27887@angie.orcam.me.uk>
To:     "Maciej W. Rozycki" <macro@orcam.me.uk>
Precedence: bulk


> 2023=E5=B9=B45=E6=9C=8819=E6=97=A5 23:51=EF=BC=8CMaciej W. Rozycki =
<macro@orcam.me.uk> =E5=86=99=E9=81=93=EF=BC=9A
>=20
> On Fri, 19 May 2023, Jiaxun Yang wrote:
>=20
>>> Given the circumstances I think this should be `panic'.  You don't =
want=20
>>> to continue with a system that can randomly lock up.
>>=20
>> I just checked how other architectures handle such situation, it =
seems like
>> TAINT_CPU_OUT_OF_SPEC is a better option.
>=20
> That can be easily missed, just as a random message in the kernel log,=20=

> even at a high priority, and LOGLEVEL_ERR is not particularly high =
even. =20
> For a system configuration that qualifies as not usable for any =
practical=20
> purpose I find this approach leaving something to desire.

Just found another reason that not to panic in such situation when I=E2=80=
=99m playing
around QEMU.

Emulation software like QEMU, mipssim, OVPSim, IASIM tends use base PRID
of a core. It can be more than annoying for people to find kernel =
suddenly won=E2=80=99t
boot on their simulator.

>=20
>> Panic in cpu_probe can be frustrating for users as it is earlier than =
initialisation
>> of consoles so the panic message can never be read by users.
>=20
> Is there no early console support for the systems affected?

For routers it=E2=80=99s very common that serial port available to user =
is not the same one
as we hooked for earlyprintk.

For QEMU users potentially using graphic interface, initialisation of =
DRM/FBDEV
comes very later.

Thanks
- Jiaxun

>=20
>  Maciej