mfd: tps6586x: Handle interrupts on suspend

mfd: tps6586x: Handle interrupts on suspend

The tps6586x driver creates an irqchip that is used by its various child
devices for managing interrupts. The tps6586x-rtc device is one of its
children that uses the tps6586x irqchip. When using the tps6586x-rtc as
a wake-up device from suspend, the following is seen:

 PM: Syncing filesystems ... done.
 Freezing user space processes ... (elapsed 0.001 seconds) done.
 OOM killer disabled.
 Freezing remaining freezable tasks ... (elapsed 0.000 seconds) done.
 Disabling non-boot CPUs ...
 Entering suspend state LP1
 Enabling non-boot CPUs ...
 CPU1 is up
 tps6586x 3-0034: failed to read interrupt status
 tps6586x 3-0034: failed to read interrupt status

The reason why the tps6586x interrupt status cannot be read is because
the tps6586x interrupt is not masked during suspend and when the
tps6586x-rtc interrupt occurs, to wake-up the device, the interrupt is
seen before the i2c controller has been resumed in order to read the
tps6586x interrupt status.

The tps6586x-rtc driver sets it's interrupt as a wake-up source during
suspend, which gets propagated to the parent tps6586x interrupt.
However, the tps6586x-rtc driver cannot disable it's interrupt during
suspend otherwise we would never be woken up and so the tps6586x must
disable it's interrupt instead.

Prevent the tps6586x interrupt handler from executing on exiting suspend
before the i2c controller has been resumed by disabling the tps6586x
interrupt on entering suspend and re-enabling it on resuming from
suspend.

Cc: stable@vger.kernel.org
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>