linux-kernel - Re: [PATCH] x86 tsc: Add the Intel Denverton Processor to native_calibrate

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Date:   Sun, 22 Jan 2017 10:33:19 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Len Brown <lenb@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Len Brown <len.brown@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86 tsc: Add the Intel Denverton Processor to
 native_calibrate_tsc()


* Len Brown <lenb@...nel.org> wrote:

> From: Len Brown <len.brown@...el.com>
> 
> The Intel Denverton microserver uses a 25 MHz TSC crystal,
> so we can derive its exact * TSC frequency
> using CPUID and some arithmetic, eg.
> 
> TSC: 1800 MHz (25000000 Hz * 216 / 3 / 1000000)
> 
> * 'exact' is only as good as the crystal, which should be +/- 20ppm
> 
> Signed-off-by: Len Brown <len.brown@...el.com>
> ---
>  arch/x86/kernel/tsc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 46b2f41f8b05..b3e397a0f29d 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -694,6 +694,7 @@ unsigned long native_calibrate_tsc(void)
>  			crystal_khz = 24000;	/* 24.0 MHz */
>  			break;
>  		case INTEL_FAM6_SKYLAKE_X:
> +		case INTEL_FAM6_ATOM_DENVERTON:
>  			crystal_khz = 25000;	/* 25.0 MHz */
>  			break;
>  		case INTEL_FAM6_ATOM_GOLDMONT:

Already upstream, as per:

  695085b4bc76 x86/tsc: Add the Intel Denverton Processor to native_calibrate_tsc()

Thanks,

	Ingo