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Date:   Tue, 30 May 2023 15:41:27 +0300
From:   Serge Semin <fancer.lancer@gmail.com>
To:     "Maciej W. Rozycki" <macro@orcam.me.uk>
Cc:     Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Paul Cercueil <paul@crapouillou.net>,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        linux-kernel@vger.kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Subject: Re: [PATCH 1/2] MIPS: Allow MIPS32R2 kernel to run on P5600 and M5150
Message-ID: <20230530124127.z5rr5vauw43rafrt@mobilestation>
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On Tue, May 30, 2023 at 01:16:32PM +0100, Maciej W. Rozycki wrote:
> 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.

I may have misunderstood something, but it seems like there is no such
problem on my P5600 system:

[fancer@mobilestation] kernel $ grep -r P5600 -B2 -A2 arch/mips/mm/c-r4k.c 
        case CPU_1004K:
        case CPU_INTERAPTIV:
        case CPU_P5600:
        case CPU_PROAPTIV:
        case CPU_M5150:
--
        case CPU_P6600:
        case CPU_M6250:
                pr_info("MIPS P5600 is here\n");
                if (!(read_c0_config7() & MIPS_CONF7_IAR) &&
                    (c->icache.waysize > PAGE_SIZE))

Log:
[    0.000000] Linux version 6.4.0-rc1-bt1-00235-gf9efd6b74b12-dirty (fancer@mobilestation) (mipsel-baikal-linux-gcc (GCC) 7.3.0, GNU ld (GNU Binutils) 2.30.0.20180208) #1
275 SMP PREEMPT Tue May 30 15:30:48 MSK 2023
[    0.000000] CPU0 revision is: 0001a830 (MIPS P5600)
[    0.000000] FPU revision is: 30f30320
[    0.000000] MSA revision is: 00000320
...
[    0.000000] VPE topology {1,1} total 2
[    0.000000] MIPS P5600 is here
...

-Serge(y)

> 
>   Maciej