Hi,
On 02/14/2017 05:23 PM, Sergei Shtylyov wrote:
> 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@xxxxxxxxxx>
>> Cc: x86@xxxxxxxxxx
>> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
>> ---
>> 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.
Sure.
Best regards,
Lu Baolu
>
>> + 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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