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 11:18:56 +0300
From:   Paul Cercueil <paul@...pouillou.net>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     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

Hi Maciej,

Le mardi 30 mai 2023 à 09:03 +0100, Maciej W. Rozycki a écrit :
> On Mon, 29 May 2023, Jiaxun Yang wrote:
> 
> > M5150 and P5600 are two MIPS32R5 kernels, however as MIPS32R5 is
> > backward compatible with MIPS32R2 there is no reason to forbid
> > M5150 and P5600 on MIPS32R2 kernel.
> 
>  What problem are you trying to solve?  The CONFIG_SYS_HAS_CPU_*
> settings 
> denote overall platform's support for the given CPU and have nothing
> to do 
> with what architecture level a given kernel has been configured for. 
> You 
> do need to get the settings right for your platform, just as you do
> in 
> 2/2, but this 1/2 part looks wrong to me.
> 
>  NB CPU_4KEC is double-listed as R1 and R2 because early revisions of
> the 
> 4KEc core were actually R1 before switching to R2, so this CPU can
> report 
> either revision.
> 
>  I don't know why CPU_XBURST is also listed as both R1 and R2, the
> history 
> looks convoluted with no explanation.  Paul, is the CPU also dual-
> revision 
> or is it just a bug and it is supposed to be listed under one ISA
> revision
> only, presumably R2?

The XBurst CPU is R1 in older Ingenic SoCs (JZ4760B and older), and R2
in newer SoCs (JZ4770 and newer).

Cheers,
-Paul