timer: hpet: don't force TIMER_READS_ITS_FREQUENCY_AT_RUNTIME

This allows the HPET timer to use kconfig to specify clock
frequency instead of relying on calculation at runtime.
When the frequency is known at build, this allow the toolchain
to optimize some calculations.

Signed-off-by: Daniel Leung <[email protected]>

Author: dcpleung

drivers/timer/Kconfig

@@ -82,7 +82,7 @@ config HPET_TIMER
 	depends on X86
 	select IOAPIC if X86
 	select LOAPIC if X86
-	select TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
+	imply TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
 	select TICKLESS_CAPABLE
 	help
 	  This option selects High Precision Event Timer (HPET) as a

drivers/timer/hpet.c

@@ -50,11 +50,22 @@ DEVICE_MMIO_TOPLEVEL_STATIC(hpet_regs, DT_DRV_INST(0));
 #define HPET_CMP_MIN_DELAY		(1000)
 #endif
 
+#define MAX_TICKS			0x7FFFFFFFUL
+
 static __pinned_bss struct k_spinlock lock;
-static __pinned_bss unsigned int max_ticks;
-static __pinned_bss unsigned int cyc_per_tick;
 static __pinned_bss unsigned int last_count;
 
+#ifdef CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
+static __pinned_bss unsigned int cyc_per_tick;
+static __pinned_bss unsigned int max_ticks;
+#else
+#define cyc_per_tick			\
+	(CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC / CONFIG_SYS_CLOCK_TICKS_PER_SEC)
+
+#define max_ticks			\
+	((MAX_TICKS - cyc_per_tick) / cyc_per_tick)
+#endif /* CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME */
+
 __isr
 static void hpet_isr(const void *arg)
 {
@@ -124,6 +135,8 @@ int sys_clock_driver_init(const struct device *dev)
 	uint32_t hz;
 
 	ARG_UNUSED(dev);
+	ARG_UNUSED(hz);
+	ARG_UNUSED(z_clock_hw_cycles_per_sec);
 
 	DEVICE_MMIO_TOPLEVEL_MAP(hpet_regs, K_MEM_CACHE_NONE);
 
@@ -133,10 +146,14 @@ int sys_clock_driver_init(const struct device *dev)
 	set_timer0_irq(DT_INST_IRQN(0));
 	irq_enable(DT_INST_IRQN(0));
 
+#ifdef CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME
 	hz = (uint32_t)(HPET_COUNTER_CLK_PERIOD / CLK_PERIOD_REG);
 	z_clock_hw_cycles_per_sec = hz;
 	cyc_per_tick = hz / CONFIG_SYS_CLOCK_TICKS_PER_SEC;
 
+	max_ticks = (MAX_TICKS - cyc_per_tick) / cyc_per_tick;
+#endif
+
 	/* Note: we set the legacy routing bit, because otherwise
 	 * nothing in Zephyr disables the PIT which then fires
 	 * interrupts into the same IRQ.  But that means we're then
@@ -148,7 +165,6 @@ int sys_clock_driver_init(const struct device *dev)
 	TIMER0_CONF_REG &= ~TCONF_FSB_EN;
 	TIMER0_CONF_REG |= TCONF_MODE32;
 
-	max_ticks = (0x7fffffff - cyc_per_tick) / cyc_per_tick;
 	last_count = MAIN_COUNTER_REG;
 
 	TIMER0_CONF_REG |= TCONF_INT_ENABLE;