stm32/hwtimer32: Check if interrupts are disabled when setting timestamp

CL:3347658 introduces disabling interrupts when setting new timestamp to
the timer. To make sure that __hw_clock_source_set() won't be used with
enabled interrupts let's add ASSERT which will check that.

This patch also adds explaination, why clearing all status bits in the
timer is correct.

BUG=b:200828093
BRANCH=none
TEST=Compile EC with CONFIG_CMD_FORCETIME enabled. Use 'forcetime'
     command to set time, then use 'timerinfo' to check if correct
     time is set.

Signed-off-by: Patryk Duda <pdk@semihalf.com>
Change-Id: I2945edbe71e4e9991b4e8eaa462d8c1d08a22d23
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3395878
Reviewed-by: Tom Hughes <tomhughes@chromium.org>

1 files changed, 15 insertions, 5 deletions

diff --git a/chip/stm32/hwtimer32.c b/chip/stm32/hwtimer32.c
index aeaa0c9ad1..f4c1fe598f 100644
--- a/chip/stm32/hwtimer32.c
+++ b/chip/stm32/hwtimer32.c
@@ -46,6 +46,8 @@ uint32_t __hw_clock_source_read(void)
 
 void __hw_clock_source_set(uint32_t ts)
 {
+	ASSERT(!is_interrupt_enabled());
+
 	/*
 	 * Stop counter to avoid race between setting counter value
 	 * and clearing status.
@@ -55,7 +57,16 @@ void __hw_clock_source_set(uint32_t ts)
 	/* Set counter value */
 	STM32_TIM32_CNT(TIM_CLOCK32) = ts;
 
-	/* Clear status */
+	/*
+	 * Clear status. We may clear information other than timer overflow
+	 * (eg. event timestamp was matched) but:
+	 * - Bits other than overflow are unused (see __hw_clock_source_irq())
+	 * - After setting timestamp software will trigger timer interrupt using
+	 *   task_trigger_irq() (see force_time() in common/timer.c).
+	 *   process_timers() is called from timer interrupt, so if "match" bit
+	 *   was present in status (think: some task timers are expired)
+	 *   process_timers() will handle that correctly.
+	 */
 	STM32_TIM_SR(TIM_CLOCK32) = 0;
 
 	/* Start counting */
@@ -239,13 +250,12 @@ int __hw_clock_source_init(uint32_t start_t)
 	/* Set up the overflow interrupt */
 	STM32_TIM_DIER(TIM_CLOCK32) = 0x0001;
 
+	/* Override the count with the start value */
+	STM32_TIM32_CNT(TIM_CLOCK32) = start_t;
+
 	/* Start counting */
 	STM32_TIM_CR1(TIM_CLOCK32) |= 1;
 
-	/* Override the count with the start value now that counting has
-	 * started. */
-	__hw_clock_source_set(start_t);
-
 	/* Enable timer interrupts */
 	task_enable_irq(IRQ_TIM(TIM_CLOCK32));