x86: Save TSC frequency in the global data

Return the saved TSC frequency in get_tbclk_mhz().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

arch/x86/include/asm/global_data.h

@@ -21,6 +21,7 @@ struct arch_global_data {
 	uint64_t tsc_base;		/* Initial value returned by rdtsc() */
 	uint32_t tsc_base_kclocks;	/* Initial tsc as a kclocks value */
 	uint32_t tsc_prev;		/* For show_boot_progress() */
+	uint32_t tsc_mhz;		/* TSC frequency in MHz */
 	void *new_fdt;			/* Relocated FDT */
 	uint32_t bist;			/* Built-in self test value */
 };

arch/x86/lib/tsc_timer.c

@@ -293,6 +293,9 @@ unsigned __attribute__((no_instrument_function)) long get_tbclk_mhz(void)
 {
 	unsigned long fast_calibrate;
 
+	if (gd->arch.tsc_mhz)
+		return gd->arch.tsc_mhz;
+
 	fast_calibrate = try_msr_calibrate_tsc();
 	if (fast_calibrate)
 		return fast_calibrate;
@@ -301,6 +304,7 @@ unsigned __attribute__((no_instrument_function)) long get_tbclk_mhz(void)
 	if (!fast_calibrate)
 		panic("TSC frequency is ZERO");
 
+	gd->arch.tsc_mhz = fast_calibrate;
 	return fast_calibrate;
 }