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SubjectRe: [PATCH v7 1/5] x86: add simple udelay calibration
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Hello!

On 2/14/2017 5:27 AM, Lu Baolu wrote:

> Add a simple udelay calibration in x86 architecture-specific
> boot-time initializations. This will get a workable estimate
> for loops_per_jiffy. Hence, udelay() could be used after this
> initialization.
>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: x86@kernel.org
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 4cfba94..aab7faa 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -835,6 +835,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
> return 0;
> }
>
> +static void __init simple_udelay_calibration(void)
> +{
> + unsigned int tsc_khz, cpu_khz;
> + unsigned long lpj;
> +
> + if (!boot_cpu_has(X86_FEATURE_TSC))
> + return;
> +
> + cpu_khz = x86_platform.calibrate_cpu();
> + tsc_khz = x86_platform.calibrate_tsc();
> +
> + tsc_khz = tsc_khz ? : cpu_khz;

Why not:

if (!tsc_khz)
tsc_khz = cpu_khz;

It's more clear IMHO.

> + if (!tsc_khz)
> + return;
> +
> + lpj = tsc_khz * 1000;
> + do_div(lpj, HZ);
> + loops_per_jiffy = lpj;
> +}
> +
> /*
> * Determine if we were loaded by an EFI loader. If so, then we have also been
> * passed the efi memmap, systab, etc., so we should use these data structures
[...]

MBR, Sergei

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