[PATCH] OMAP4: clockdomain: Follow recommended enable sequence

[Paul Walmsley]

On Fri, 1 Apr 2011, Rajendra Nayak wrote:

> On 4/1/2011 8:21 PM, Rajendra Nayak wrote:
> > > > In omap_hwmod.c:_enable(), what do you think about:
> > > > 
> > > > 1. saving the current idle mode of the clockdomain,
> > > > 
> > > > 2. forcing the clockdomain to software-supervised wakeup.
> > > > 
> > > > 3. enabling clocks and waiting for the module as we currently do, then
> > > > 
> > > > 4. switching the clockdomain's idle mode back to its original state?
> > > > 
> > > > Seems like that would be a reasonable approach for the short term, at
> > > > least for drivers that have been converted to PM runtime.
> > > 
> > > Ok, I'll try and get some RFC patches in these lines soon.
> > 
> > I tried some of what you were suggesting here and it seems to
> > work well, like you said, for the drivers which are converted
> > to PM runtime.
> > 
> > Now the issue seems to be, how do we handle the ones which
> > are *still* using clock framework to enable main clocks and
> > are yet to be converted to PM runtime.
> > 
> > One such, MMC, is showing me issues on OMAP4 even at boot
> > and causes a crash.
> > 
> > Its a different thing that some of these drivers which use
> > direct clock calls are working by fluke on OMAP4 since the
> > clock framework does not even wait for the modules to become
> > accessible after the clock enable.
> >
> > I know the right way seems to be to get all these drivers
> > converted to PM runtime, but that might take sometime.
> 
> One way I am able to get this working (atleast MMC)
> is by preventing the clock domain belonging to MMC module
> from being programmed into HW_SUP mode.

What programs the OMAP4 clockdomains into hwsup mode in the first place?  
There's no clkdms_setup() as there is in mach-omap2/pm34xx.c.  I guess 
maybe this code in mach-omap2/pm.c might do it as a side effect:

	switch (sleep_switch) {
	case FORCEWAKEUP_SWITCH:
		if (pwrdm->pwrdm_clkdms[0]->flags & CLKDM_CAN_ENABLE_AUTO)
			clkdm_allow_idle(pwrdm->pwrdm_clkdms[0]);
		else
			clkdm_sleep(pwrdm->pwrdm_clkdms[0]);
		break;

If I'm reading this code correctly, it will always force clockdomains that 
support hwsup mode into hwsup mode, even if they've been previously 
programmed to swsup mode.  That's not right.  This function should leave 
the clockdomain's autoidle setting where it was when the function was 
entered.  So this needs to be fixed also.

> Acceptable hack in the interim while we wait for the MMC driver to be 
> using PM runtime?

Ideally this should be overridden in the code, not the data, since this 
hack is needed due to a software problem, not a hardware problem.  The 
clockdomains data should just be a statement of what the hardware 
supports.

But given the above bug and the lack of some clkdms_setup() function for 
OMAP4, I guess the clockdomains data is the least bad choice for right 
now, provided that the patch also:

1. puts a big comment in that data warning about the problem and 
explaining why

2. puts a pr_warn() in mach-omap2/pm44xx.c:omap4_pm_init() saying: 
"WARNING: OMAP4 power savings limited since MMC driver not converted to 
PM runtime"


- Paul