linux-kernel - Re: [PATCH] x86: better CPU identification without the CPUID

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Date:	Sat, 13 Sep 2008 21:43:59 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Krzysztof Helt" <krzysztof.h1@...pl>
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com
Subject: Re: [PATCH] x86: better CPU identification without the CPUID

On Sat, Sep 13, 2008 at 3:56 AM, Krzysztof Helt <krzysztof.h1@...pl> wrote:
> From: Krzysztof Helt <krzysztof.h1@...pl>
>
> cpus without the CPUID instruction are identified
> as general 386 or 486 while some cpus (mostly made
> by Cyrix) provide c_identify function which identify
> correctly older cpus using cpu specific registers).
>
> Cyrix cpus are even worse as 5x86 and 6x68 have
> the CPUID instruction disabled. The CPUID is
> enabled by the c_identify() but the c_identify
> is only called when the CPUID is available.
>
> Fix this by calling the c_identify() for all known
> cpu families if there is no the CPUID instruction
>
> Signed-off-by: Krzysztof Helt <krzysztof.h1@...pl>
> ---
>
> I have tested it on Cyrix Cx486DX2 cpu.
>
> I suspect that coma_bug field and mtrr support is not
> set correctly for the Cyrix 6x86 family. I have not a cpu from
> the Cyrix 6x68 family to test.
>
> The code path is (+ where the patch code is added)
>
> if (have_cpuid_p()) {
>
> }
> + } else {
> ...
> + }
>
> so it does not affect cpus with the CPUID instruction.
>
> Regards,
> Krzysztof
>
> diff -urp linux-mm/arch/x86/kernel/cpu/common.c linux-486/arch/x86/kernel/cpu/common.c
> --- linux-mm/arch/x86/kernel/cpu/common.c       2008-09-05 23:38:20.295563396 +0200
> +++ linux-486/arch/x86/kernel/cpu/common.c      2008-09-12 22:53:27.062265329 +0200
> @@ -444,6 +444,17 @@ static void __cpuinit generic_identify(s
>
>                init_scattered_cpuid_features(c);
>                detect_nopl(c);
> +       } else {
> +               int i;
> +               for (i = 0; i < X86_VENDOR_NUM; i++)
> +                       if (cpu_devs[i] && cpu_devs[i]->c_identify) {
> +                               c->x86_vendor_id[0] = 0;
> +                               cpu_devs[i]->c_identify(c);
> +                               if (c->x86_vendor_id[0]) {
> +                                       get_cpu_vendor(c, 0);
> +                                       break;
> +                               }
> +                       }
>        }
>  }
>
> --

1. can you check tip/master?
2. please check if you can add code in early_identify_cpu
3. need to move c_identify_cpu calling to identify_cpu

YH
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