[PATCHv4 6/8] ARM: OMAP4: PM: support ret_logic/mem_off_counters

[Tero Kristo]

On Wed, 2012-05-02 at 10:45 +0200, Bedia, Vaibhav wrote:
> Hi Tero,
> 
> On Fri, Apr 20, 2012 at 14:49:49, Kristo, Tero wrote:
> > From: Axel Haslam <axelhaslam at gmail.com>
> > 
> > On OMAP4, there is no support to read previous logic state
> > or previous memory state achieved when a power domain transitions
> > to RET. Instead there are module level context registers.
> > 
> > In order to support the powerdomain level logic/mem_off_counters
> > on OMAP4, instead use the previous power state achieved (RET) and
> > the *programmed* logic/mem RET state to derive if a powerdomain lost
> > logic or did not.
> > 
> > If the powerdomain is programmed to enter RET state and lose logic
> > in RET state, knowing that the powerdomain entered RET is good enough
> > to derive that the logic was lost as well, in such cases.
> > 
> 
> Unfortunately this won't scale for AM33xx devices :(
> It neither has module level context registers nor previous logic/memory state
> registers in PRCM. 
> 
> At a top level, there's a Cortex-M3 (CM3) to assist the low power state transitions
> and the indication of successful transition to a low power states is handled as part
> of the IPC mechanism between the MPU (A8) and CM3 which is s/w defined.
> 
> Since the various APIs like omap_hwmod_get_context_loss_context() and friends are
> necessary to have correct context saves and restores in drivers we'll need
> to add another API for AM33xx which basically builds on the IPC mechanism
> and updates the counters.
> 
> So, instead of the fallback mechanism that is currently in place, can the
> implementation for updating the logic/mem counters be converted to make use of
> function pointers. When AM33xx PM support comes in, we can just define
> a custom function and not pollute the code with cpu_is_* checks.

I think that should be fine. We can add arch_hwmod struct or such
(similar to arch_clkdm / arch_pwrdm) if need be. However, I think we
should just expand the support towards that way once we can implement
the am33xx support properly with a separate patch. I guess this doesn't
break anything on am33xx currently, right?

-Tero