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>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 4bf0c8926a1c061bb22c1973962a0d668bfa3d98..e70204e13e48c24158582ccd2781603b0af28538 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -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