drivers: timer: WCH system timer fixes

Use a spinlock to be sure we're consistently returning monotonically
increasing time, and not accessing the periperal or local count and
then have them changed out from under us in the ISR. Also tweak the init
ordering a bit to ensure IRQs are enabled before enabling the peripheral.

Signed-off-by: Peter Johanson <peter@peterjohanson.com>

Author: petejohanson

drivers/timer/wch_systick_ch32v00x.c

@@ -10,12 +10,11 @@
 #include <zephyr/drivers/timer/system_timer.h>
 #include <zephyr/irq.h>
 #include <zephyr/kernel.h>
+#include <zephyr/spinlock.h>
 #include <zephyr/sys/util.h>
 
 #include <hal_ch32fun.h>
 
-#define STK_SWIE  BIT(31)
-#define STK_STRE  BIT(3)
 #define STK_STCLK BIT(2)
 #define STK_STIE  BIT(1)
 #define STK_STE   BIT(0)
@@ -27,20 +26,36 @@
 
 #define SYSTICK ((SysTick_Type *)(DT_INST_REG_ADDR(0)))
 
+static struct k_spinlock lock;
 static volatile uint32_t ch32v00x_systick_count;
 
 static void ch32v00x_systick_irq(const void *unused)
 {
 	ARG_UNUSED(unused);
 
+	k_spinlock_key_t key = k_spin_lock(&lock);
+
+	SYSTICK->CTLR &= ~(STK_STE);
 	SYSTICK->SR = 0;
+	SYSTICK->CNT = 0;
+	SYSTICK->CTLR |= STK_STE;
+
 	ch32v00x_systick_count += CYCLES_PER_TICK; /* Track cycles. */
+
+	k_spin_unlock(&lock, key);
 	sys_clock_announce(1);                     /* Poke the scheduler. */
 }
 
 uint32_t sys_clock_cycle_get_32(void)
 {
-	return ch32v00x_systick_count + SYSTICK->CNT;
+	uint32_t ret;
+
+	k_spinlock_key_t key = k_spin_lock(&lock);
+
+	ret = ch32v00x_systick_count + SYSTICK->CNT;
+	k_spin_unlock(&lock, key);
+
+	return ret;
 }
 
 uint32_t sys_clock_elapsed(void)
@@ -52,13 +67,15 @@ static int ch32v00x_systick_init(void)
 {
 	IRQ_CONNECT(DT_INST_IRQN(0), 0, ch32v00x_systick_irq, NULL, 0);
 
+	SYSTICK->CTLR = 0;
 	SYSTICK->SR = 0;
 	SYSTICK->CMP = CYCLES_PER_TICK;
 	SYSTICK->CNT = 0;
-	SYSTICK->CTLR = STK_STRE | STK_STCLK | STK_STIE | STK_STE;
 
 	irq_enable(DT_INST_IRQN(0));
 
+	SYSTICK->CTLR = STK_STE | STK_STCLK | STK_STIE;
+
 	return 0;
 }