linux-kernel - Re: [PATCH 1/2] MIPS: Allow MIPS32R2 kernel to run on P5600 and M5150

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Date:   Tue, 30 May 2023 16:33:48 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     "Maciej W. Rozycki" <macro@...am.me.uk>,
        Paul Cercueil <paul@...pouillou.net>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Subject: Re: [PATCH 1/2] MIPS: Allow MIPS32R2 kernel to run on P5600 and M5150

On Tue, May 30, 2023 at 02:10:04PM +0100, Jiaxun Yang wrote:
> 
> 
> > 2023年5月30日 13:16，Maciej W. Rozycki <macro@...am.me.uk> 写道：
> > 
> > On Tue, 30 May 2023, Jiaxun Yang wrote:
> > 
> >>> Sure, but this change is not needed for it.  You just need to declare 
> >>> which ISA revisions your platform supports and leave `__get_cpu_type' 
> >>> alone.  It has worked like that for a decade now.
> >> 
> >> I’m afraid it won’t work as you expected.
> >> 
> >> Actually I ran into a problem that `case CPU_P5600` in c-r4k.c is optimised out
> >> by compiler, because the codepath is marked as unreachable.
> > 
> > Maybe there's a bug elsewhere then.  Send me your .config and I'll try to 
> > reproduce it.
> 

> Ok I see the problem, after applying patch 2 the issue is gone.
> So actually only patch 2 is necessary.
> 
> The unreachable mark here leads gcc to generate some confusing code
> and I misread it.
> 
> Sorry for the noise.

Great! Indeed enabling the SYS_HAS_CPU_MIPS32_R5 config is enough to
stop the CPU_P5600 being optimized out. Thanks for your work. Let me
know if you need some tests on another instance of the P5600 hw.

-Serge(y)

> 
> Thanks
> - Jiaxun
> 
> > 
> >  Maciej
>