linux-kernel - Re: [PATCH] MIPS: add support for buggy MT7621S core detection

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Message-ID: <CALCv0x0SwiOAWXk36vuFkspNSM16nS=wdMhm5ZNyOdFUia5zuw@mail.gmail.com>
Date:   Mon, 5 Apr 2021 18:54:26 -0700
From:   Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Wei Li <liwei391@...wei.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        linux-mips@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Felix Fietkau <nbd@....name>
Subject: Re: [PATCH] MIPS: add support for buggy MT7621S core detection

On Mon, Apr 5, 2021 at 6:22 PM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
> On Fri, 2 Apr 2021, Ilya Lipnitskiy wrote:
>
> > diff --git a/arch/mips/include/asm/bugs.h b/arch/mips/include/asm/bugs.h
> > index d72dc6e1cf3c..d32f0c4e61f7 100644
> > --- a/arch/mips/include/asm/bugs.h
> > +++ b/arch/mips/include/asm/bugs.h
> > @@ -50,4 +51,21 @@ static inline int r4k_daddiu_bug(void)
> >       return daddiu_bug != 0;
> >  }
> >
> > +static inline void cm_gcr_pcores_bug(unsigned int *ncores)
> > +{
> > +     struct cpulaunch *launch;
> > +
> > +     if (!IS_ENABLED(CONFIG_SOC_MT7621) || !ncores)
> > +             return;
> > +
> > +     /*
> > +      * Ralink MT7621S SoC is single core, but GCR_CONFIG always reports 2 cores.
>
>  Overlong line.
>
> > diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
> > index bcd6a944b839..e1e9c11e8a7c 100644
> > --- a/arch/mips/kernel/smp-cps.c
> > +++ b/arch/mips/kernel/smp-cps.c
> > @@ -60,6 +61,7 @@ static void __init cps_smp_setup(void)
> >               pr_cont("{");
> >
> >               ncores = mips_cps_numcores(cl);
> > +             cm_gcr_pcores_bug(&ncores);
> >               for (c = 0; c < ncores; c++) {
> >                       core_vpes = core_vpe_count(cl, c);
> >
> > @@ -170,6 +172,7 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
> >
> >       /* Allocate core boot configuration structs */
> >       ncores = mips_cps_numcores(0);
> > +     cm_gcr_pcores_bug(&ncores);
>
>  Why called at each `mips_cps_numcores' call site rather than within the
> callee?  Also weird inefficient interface: why isn't `ncores' passed by
> value for a new value to be returned?
Thanks for the comments. Including asm/bugs.h in asm/mips-cps.h led to
some circular dependencies when I tried it, but I will try again based
on your feedback - indeed it would be much cleaner to have this logic
in mips_cps_numcores. The only wrinkle is that mips_cps_numcores may
return a different value on MT7621 after the cores have started due to
CPULAUNCH flags changing, but nobody calls mips_cps_numcores later
anyway, so it's a moot point today. I will clean up the change and
resend.

Ilya