drivers/timer/hpet: Work around crazy qemu behavior (bab348e9) · Commits · Wenxi XU / zephyr

At least twice (to be fair: twice among thousands of test runs), I've seen this device return "backwards" times in SMP, where the counter value read from one CPU is behind the saved value already seen on the other. On hardware this should obviously never happen, HPET is a single global device. Add a simple workaround on QEMU targets so the math doesn't blow up. Signed-off-by:

Andy Ross <andrew.j.ross@intel.com>

drivers/timer/hpet.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -38,6 +38,20 @@ static void hpet_isr(void *arg)
		ARG_UNUSED(arg);
		k_spinlock_key_t key = k_spin_lock(&lock);
		u32_t now = MAIN_COUNTER_REG;

		if (IS_ENABLED(CONFIG_SMP) &&
		IS_ENABLED(CONFIG_QEMU_TARGET)) {
		/* Qemu in SMP mode has observed the clock going
		* "backwards" relative to interrupts already received
		* on the other CPU, despite the HPET being
		* theoretically a global device.
		*/
		s32_t diff = (s32_t)(now - last_count);

		if (last_count && diff < 0) {
		now = last_count;
		}
		}
		u32_t dticks = (now - last_count) / cyc_per_tick;

		last_count += dticks * cyc_per_tick;

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