[PATCH] rtc: armada38x: Fix concurrency access in armada38x_rtc_set_time

[Andrew Lunn]

On Wed, Apr 15, 2015 at 03:13:53PM +0200, Gregory CLEMENT wrote:
> While setting the time, the RTC TIME register should not be
> accessed. However due to hardware constraints, setting the RTC time
> involves sleeping during 100ms. This sleep was done outside the
> critical section protected by the spinlock, so it was possible to read
> the RTC TIME register and get an incorrect value. This patch
> introduces a mutex for protecting the RTC TIME access, unlike the
> spinlock it is allowed to sleep in a critical section protected by a
> mutex. The RTC STATUS register can still be used from the interrupt
> handler but it has no effect on setting the time.

Hi Gregory

There is the following comment in the code:

        /*
         * Setting the RTC time not always succeeds. According to the
         * errata we need to first write on the status register and
         * then wait for 100ms before writing to the time register to be
         * sure that the data will be taken into account.
         */

The interrupt handler also writes to the STATUS register. So what
happens if there is an interrupt during that 100ms and a second write
to STATUS?

Maybe it is necessary to disable the RTC interrupt while setting the
time?

	Andrew