[PATCH 1/6] omap4: powerdomain: Add supported INACTIVE power state

-----Original Message-----
From: Paul Walmsley [mailto:paul at pwsan.com]
Sent: Tuesday, February 01, 2011 4:44 AM
To: Santosh Shilimkar
Cc: linux-omap at vger.kernel.org; khilman at ti.com; b-cousson at ti.com;
rnayak at ti.com; linux-arm-kernel at lists.infradead.org
Subject: Re: [PATCH 1/6] omap4: powerdomain: Add supported INACTIVE
power state

Hello Santosh,

On Fri, 28 Jan 2011, Santosh Shilimkar wrote:

quoted

On OMAP4, one can explicitly program INACTIVE as the power state

of

quoted

the logic area inside the power domain. Techincally PD state

programmed

quoted

to ON and if all the clock domains within the PD are idled, is

equivalent

quoted

tp PD programmed to INACTIVE and all the clock domains within the

PD are

quoted

idled. There won't be any power difference in above two.

Since the CPUIDLE C-states explicitly make use of INACTIVE as a PD
targeted state and also there is some additional latancy involved
with PD INACTIVE vs PD ON, it's better to support it as an explcit
PD state.

This patch adds the support to allow explicit PD INACTIVE
programming if supported.

What does the hardware do when the powerdomain is programmed to
INACTIVE?
Does it actually force the clockdomains idle?

No. It doesn't force it. The power domain to hit INACTIVE, the
clockdomain within the power domain needs to idle and it is
still a prerequisite. With INACTIVE being programmed, we could
issue a sleep transition.

PD_ON:
No power transition, only clocks are gated. Power domain stays ON.

PD_INA:
Power domain transitions to INACTIVE state. All logic and
memory stay powered. This state allows for a voltage
sleep transition.

Regards,
Santosh