[PATCH 2/2] ARM: vf610: Use ARM Global Timer as clocksource

On Thu, Sep 25, 2014 at 10:25:13AM +0200, Stefan Agner wrote:

Am 2014-09-25 09:50, schrieb Shawn Guo:

quoted

On Thu, Sep 11, 2014 at 02:06:15PM +0200, Stefan Agner wrote:

quoted

Use ARM Global Timer as clocksource instead of the PIT timer. This
leaves the PIT timer for other users e.g. the secondary Cortex-M4
core. Also, the Global Timer has double the precission (running at
pheripheral clock compared to IPG clock) and a 64-bit incrementing
counter register.

I just think of one thing.  Will this change cause a problem of the low
power idle support in case we want to power down ARM core in there?

I'm not sure what really happend to the Global Timer when we power down
the ARM core. We use a clocksoure of different power domain now, so it
might make a difference in low power modes, but I think it will improve
things: The PIT timer's clock currently have been clock gated even in
STOP mode, which does not power down the ARM core. And it would be shut
down completely in LP-Mode 1-3 which since PIT is part of the big power
domain 1. 

But AFAIK, its not required that the clocksource is running while in low
power modes. The time should just not jump, and if the timers registers
are lost during suspend, a proper suspend/resume support need to be
implemented. 

Sorry, I should be more specific in the first place.  What I'm concerned
is more about clockevent than clocksource.  If some day we have a
cpuidle driver for vf610, which powers off ARM core in a deep C-state,
the clockevent device will be gone as long as system enters the C-state,
and no timer interrupt can wake up the core from idle state.

Shawn