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Date:   Tue, 30 May 2023 15:51:00 +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: <20230530125100.bd626syvkbfv7zhv@mobilestation>
References: <20230529135245.4085-1-jiaxun.yang@flygoat.com>
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On Tue, May 30, 2023 at 03:41:30PM +0300, Serge Semin wrote:
> 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
> ...

Here is the CPU-related kernel configs:
root@msbt2:~# cat /proc/config.gz | gunzip | grep CPU_MIPS
# CONFIG_CPU_MIPS32_R2 is not set
# CONFIG_CPU_MIPS32_R5 is not set
# CONFIG_CPU_MIPS32_3_5_FEATURES is not set
CONFIG_CPU_MIPS32_R5_FEATURES=y
CONFIG_CPU_MIPS32_R5_XPA=y
CONFIG_SYS_HAS_CPU_MIPS32_R2=y
CONFIG_SYS_HAS_CPU_MIPS32_R3_5=y
CONFIG_SYS_HAS_CPU_MIPS32_R5=y
CONFIG_CPU_MIPS32=y
CONFIG_CPU_MIPSR5=y
CONFIG_CPU_MIPSR2_IRQ_VI=y
CONFIG_CPU_MIPSR2_IRQ_EI=y

-Serge(y)

> 
> -Serge(y)
> 
> > 
> >   Maciej