drivers: timer: tsc: retrieve clock frequency of system timer at runtime

add support for retrieve clock frequency (HW clock cycle per sec) of
system timer at runtime by reading cpu clock via cpuid

Signed-off-by: Najumon B.A <[email protected]>

Author: najumon1980

drivers/timer/apic_tsc.c

@@ -8,12 +8,18 @@
 #include <zephyr/spinlock.h>
 #include <zephyr/drivers/interrupt_controller/loapic.h>
 #include <zephyr/irq.h>
+#include <cpuid.h>
 
 #define IA32_TSC_DEADLINE_MSR 0x6e0
 #define IA32_TSC_ADJUST_MSR   0x03b
 
+#ifdef CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
+static uint64_t CYC_PER_TICK;
+extern int z_clock_hw_cycles_per_sec;
+#else
 #define CYC_PER_TICK (CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC \
 		      / (uint64_t) CONFIG_SYS_CLOCK_TICKS_PER_SEC)
+#endif
 
 struct apic_timer_lvt {
 	uint8_t vector   : 8;
@@ -158,9 +164,11 @@ static inline void cpuid(uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *
 
 static int sys_clock_driver_init(void)
 {
-#ifdef CONFIG_ASSERT
+#if defined(CONFIG_ASSERT) || defined(CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME)
 	uint32_t eax, ebx, ecx, edx;
+#endif
 
+#ifdef CONFIG_ASSERT
 	eax = 1; ecx = 0;
 	cpuid(&eax, &ebx, &ecx, &edx);
 	__ASSERT((ecx & BIT(24)) != 0, "No TSC Deadline support");
@@ -174,6 +182,23 @@ static int sys_clock_driver_init(void)
 	__ASSERT((ebx & BIT(1)) != 0, "No TSC_ADJUST MSR support");
 #endif
 
+#ifdef CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
+	int tsc_freq;
+
+	eax = 0;
+	ebx = 0;
+	ecx = 0;
+	if (!__get_cpuid(0x15, &eax, &ebx, &ecx, &edx)) {
+		__ASSERT(false, "error cpuid leaf 0x15\n");
+	}
+
+	__ASSERT((ebx != 0) && (ecx != 0), "No TSC/core crystal clock ratio is enumerated");
+
+	tsc_freq = (uint32_t)((ecx * (uint64_t)ebx) / eax);
+	z_clock_hw_cycles_per_sec = tsc_freq;
+	CYC_PER_TICK = tsc_freq/CONFIG_SYS_CLOCK_TICKS_PER_SEC;
+#endif
+
 	clear_tsc_adjust();
 
 	/* Timer interrupt number is runtime-fetched, so can't use