[PATCHv4 5/6] ARM: OMAP3PLUS PM: Add IO Daisychain support via hwmod mux

[Tero Kristo]

On Tue, 2012-03-06 at 09:51 +0530, Rajendra Nayak wrote:
> Hi Paul,
> 
> On Tuesday 06 March 2012 09:32 AM, Paul Walmsley wrote:
> > Hi
> >
> > a few comments:
> >
> > On Fri, 2 Mar 2012, Tero Kristo wrote:
> >
> >> From: Vishwanath BS<vishwanath.bs at ti.com>
> >>
> >> IO Daisychain feature has to be triggered whenever there is a change in
> >> device's mux configuration (See section 3.9.4 in OMAP4 Public TRM vP).
> >>
> >> Now devices can idle independent of the powerdomain, there can be a
> >> window where device is idled and corresponding powerdomain can be
> >> ON/INACTIVE state. In such situations, since both module wake up is
> >> enabled at padlevel as well as io daisychain sequence is triggered,
> >> there will be 2 PRCM interrupts (Module async wake up via swakeup and
> >> IO Pad interrupt). But as PRCM Interrupt handler clears the Module
> >> Padlevel WKST bit in the first interrupt, module specific interrupt
> >> handler will not triggered for the second time
> >>
> >> Also look at detailed explanation given by Rajendra at
> >> http://www.spinics.net/lists/linux-serial/msg04480.html
> >>
> >> Signed-off-by: Vishwanath BS<vishwanath.bs at ti.com>
> >> Signed-off-by: Tero Kristo<t-kristo at ti.com>
> >> ---
> >>   arch/arm/mach-omap2/omap_hwmod.c |    9 +++++++--
> >>   arch/arm/mach-omap2/pm.c         |   15 +++++++++++++++
> >>   arch/arm/mach-omap2/pm.h         |    1 +
> >>   3 files changed, 23 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
> >> index 5192cab..56adbfb 100644
> >> --- a/arch/arm/mach-omap2/omap_hwmod.c
> >> +++ b/arch/arm/mach-omap2/omap_hwmod.c
> >
> > ...
> >
> >> @@ -1535,8 +1536,10 @@ static int _enable(struct omap_hwmod *oh)
> >>   	/* Mux pins for device runtime if populated */
> >>   	if (oh->mux&&  (!oh->mux->enabled ||
> >>   			((oh->_state == _HWMOD_STATE_IDLE)&&
> >> -			 oh->mux->pads_dynamic)))
> >> +			 oh->mux->pads_dynamic))) {
> >>   		omap_hwmod_mux(oh->mux, _HWMOD_STATE_ENABLED);
> >> +		omap_trigger_io_chain();
> >
> > Looks racy: if two hwmods with dynamic mux entries go idle at the same
> > time, or one goes idle while another one is enabled, won't the calls to
> > omap_trigger_io_chain() race?  Locking is per-hwmod and there's no locking
> > in omap_trigger_io_chain() or the functions it calls.
> 
> I agree, this needs locking to avoid races.

I'll add one for v5.

> 
> >
> > Also, won't this result in needless resets of the I/O chain?  Seems like
> > we'd only need to do this when the next power state of the enclosing
> > powerdomain will enter either RETENTION or OFF.  And even then, it
> > presumably should only happen when the last active device in that
> > powerdomain is going idle?
> 
> Yes, the module async wakeups will work as long as the power domain
> enclosing the module is not in OSWR or OFF, so ideally this trigger
> should happen only when all modules in the given powerdomain are
> disabled and we plan to program the Powerdomain down to OSWR or
> OFF state. With what we are doing today we end up with periods when we
> have multiple wakeups (a module wakeup as well as an IO wakeup).
> The last we discussed this with Kevin, there wasn't a better place where
> we could trigger this, with no usecounting at powerdomain level you
> didn't know when the last active device in the powerdomain was going
> idle.
> But now with Tero's series which adds usecounting at power/voltage
> domain level, maybe its possible, but I need to look more.
> Do you already have an idea on where this would fit better, so we
> avoid this multiple wakeup scenario?

This should be easy, we can add a hook at the pwrdm_clkdm_enable /
disable calls to check against idle / active states. However, seeing the
acceptance status for the usecounting series, we probably have to just
go ahead with the extra latency involved iochain series and make
optimizations later once the usecounting can be accepted.

Speaking of the usecounting series, Paul, did you have any time to look
at it? Also, there are still some issues seen by Kevin on that series
with omap3430 which I am unable to reproduce (I posted a couple of trial
patches for taking care of that but don't know how they behave.)

-Tero