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

[Lu Baolu]

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;
+	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
@@ -983,6 +1003,8 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	x86_configure_nx();
 
+	simple_udelay_calibration();
+
 	parse_early_param();
 
 #ifdef CONFIG_MEMORY_HOTPLUG
-- 
2.1.4