Re: [PATCH v2] clocksource: sun4i: Clear interrupts after stopping timer in probe function

On Mon, Aug 15, 2016 at 12:57:04PM +0800, Chen-Yu Tsai wrote:

The bootloader (U-boot) sometimes uses this timer for various delays.
It uses it as a ongoing counter, and does comparisons on the current
counter value. The timer counter is never stopped.

In some cases when the user interacts with the bootloader, or lets
it idle for some time before loading Linux, the timer may expire,
and an interrupt will be pending. This results in an unexpected
interrupt when the timer interrupt is enabled by the kernel, at
which point the event_handler isn't set yet. This results in a NULL
pointer dereference exception, panic, and no way to reboot.

Thanks for tracking down this bug. It bit me too once. Now I won't
wonder if it was my fault. I do wonder if there are more interrupts
which need their pending status cleared in the probe function.

-- 
Rask Ingemann Lambertsen