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x86/timers: Add simple udelay calibration 

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.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-usb@vger.kernel.org
Link: http://lkml.kernel.org/r/1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Lu Baolu 2017-03-21 16:01:29 +08:00 committed by Ingo Molnar
parent 97da3854c5
commit dd759d93f4
1 changed files with 22 additions and 0 deletions
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22
arch/x86/kernel/setup.c
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@ -837,6 +837,26 @@ 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;
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
@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p)
*/
x86_configure_nx();
simple_udelay_calibration();
parse_early_param();
#ifdef CONFIG_MEMORY_HOTPLUG