linux-kernel - Re: [PATCH] LoongArch: Use a fallback CPU model when IOCSR-based model probing fails

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Message-ID: <aBLIlNAWLbZ1hBv0@pie>
Date: Thu, 1 May 2025 01:04:20 +0000
From: Yao Zi <ziyao@...root.org>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>, Thomas Gleixner <tglx@...utronix.de>,
	Tianyang Zhang <zhangtianyang@...ngson.cn>,
	Jiaxun Yang <jiaxun.yang@...goat.com>,
	Jianmin Lv <lvjianmin@...ngson.cn>, loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Mingcong Bai <jeffbai@...c.io>,
	Kexy Biscuit <kexybiscuit@...c.io>
Subject: Re: [PATCH] LoongArch: Use a fallback CPU model when IOCSR-based
 model probing fails

On Wed, Apr 30, 2025 at 03:48:25PM +0800, Huacai Chen wrote:
> Hi, Yao Zi,
> 
> On Wed, Apr 30, 2025 at 1:41 PM Yao Zi <ziyao@...root.org> wrote:
> >
> > Reading vendor and cpuname IOCSRs yields 0x258000fff00 instead of
> > human-readable model strings on Loongson 2K0300 SoC, which messes up
> > format of /proc/cpuinfo since it represents as an empty string.
> CPUNAME IOCSR is filled by firmware and readed by kernel. If you read
> some garbage, that means you need to modify your firmware.

Thanks for the hint, I'll take a look in my firmware instead.

> And if there is completely no CPUNAME register, you need to fill it by
> FDT, see init_cpu_fullname() in arch/loongarch/kernel/env.c.
> 
> Huacai

Best regards,
Yao Zi

> >
> > Let's consider IOCSR-based model probing fails if the result model is an
> > empty string. A fallback model name is set in such cases.
> >
> > Signed-off-by: Yao Zi <ziyao@...root.org>
> > ---
> >  arch/loongarch/kernel/cpu-probe.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/loongarch/kernel/cpu-probe.c b/arch/loongarch/kernel/cpu-probe.c
> > index fedaa67cde41..785513d43696 100644
> > --- a/arch/loongarch/kernel/cpu-probe.c
> > +++ b/arch/loongarch/kernel/cpu-probe.c
> > @@ -270,12 +270,13 @@ static inline void cpu_probe_loongson(struct cpuinfo_loongarch *c, unsigned int
> >         if (!cpu_has_iocsr)
> >                 return;
> >
> > -       if (!__cpu_full_name[cpu])
> > -               __cpu_full_name[cpu] = cpu_full_name;
> > -
> >         *vendor = iocsr_read64(LOONGARCH_IOCSR_VENDOR);
> >         *cpuname = iocsr_read64(LOONGARCH_IOCSR_CPUNAME);
> >
> > +       if (!__cpu_full_name[cpu])
> > +               __cpu_full_name[cpu] = cpu_full_name[0] ? cpu_full_name :
> > +                                                         "Loongson-Unknown";
> > +
> >         config = iocsr_read32(LOONGARCH_IOCSR_FEATURES);
> >         if (config & IOCSRF_CSRIPI)
> >                 c->options |= LOONGARCH_CPU_CSRIPI;
> > --
> > 2.49.0
> >
> >