-----Original Message-----
From: Thomas, Ramesh [mailto:ramesh.thomas(a)intel.com]
Sent: Thursday, July 14, 2016 9:32 AM
To: devel(a)lists.zephyrproject.org
Subject: [devel] Re: Re: Re: Re: Re: [RFC] Power Management Infrastructure

On 7/13/2016 11:40 PM, Rahamim, Hezi wrote:

Hi Dimitriy,

The get_state is there only for symmetry and good practice.
As mentioned below the power manager service will probably not use it as it is

not efficient to do get_state to all devices to know all the devices states...

The more important part of the RFC is adding the set_state function and the

device policies.

That made me think why we originally came up with 2 functions when one was
enough. Probably we thought the same way - to keep symmetry. Problem is that
we will keep getting more needs and we will either add more functions to
device_pm_ops or will have to change existing ones.

Because, we agreed on the fact that suspend resume were managed by a central entity and was the only needed control over the drivers. I think this is still true.

[HR] Here is an example:
There are three peripherals in a certain SOC: UART, I2C and SPI.
Both I2C and SPI are fed from the same PLL and the UART from a second one.
At the beginning the three peripherals are at DEVICE_PM_ACTIVE_STATE.
The user application decides that the I2C and the SPI should go to suspend.
It then calls the set_state function of these devices with

DEVICE_PM_SUSPEND_STATE.

When idle comes the PM service is called and see that it can close the SPI and

I2C PLL.

However, it cannot move to SYS_PM_DEEP_SLEEP as the UART is still active.

In my opinion the clock tree needs to be managed completely separately, and in a completely independent way of the pm state.
Each driver mark that they use their clock when active and mark that they do not need it when not active. One can consider that an enabled clock gate is equivalent to a deep sleep forbidden, but that won't be true always on clock gates.

Will the PM service also put devices to suspend state, or only the apps will do it?
Looks like the PM Service will never enter Deep Sleep if any device is on - any
exceptions?

In the above example, the system had to go to idle for the PLL to get turned off.
If you had a central scheme to turn off clocks then the PLL could have been
turned off when both i2c and spi got turned off. Just an observation.

---------------------------------------------------------------------
Intel Corporation SAS (French simplified joint stock company)
Registered headquarters: "Les Montalets"- 2, rue de Paris,
92196 Meudon Cedex, France
Registration Number: 302 456 199 R.C.S. NANTERRE
Capital: 4,572,000 Euros

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.