i.MX28 regulator operating modes for Linux

[lategoodbye]

Hi,

i'm still working on regulator support for Linux Mainline and have some questions about the LINREGs and DC-DC on the i.MX28 PMU.

1. Which of the Linux modes (see below) could be mapped for LINREGs and DC-DC?

2. Looking at the FSL BSP (2.6.35) shows that FAST mode for LINREGs is implemented as DISABLE_STEPPING=1. Is the implementation correct?

3. Are there any useful LINREG settings for idle state?

4. What are the relevant DC-DC settings for the Linux regulator modes?

Here is a quote of the possible operating modes of a regulator (this includes also the DC-DC):

/*

* Regulator operating modes.

*

* Regulators can run in a variety of different operating modes depending on

* output load. This allows further system power savings by selecting the

* best (and most efficient) regulator mode for a desired load.

*

* Most drivers will only care about NORMAL. The modes below are generic and

* will probably not match the naming convention of your regulator data sheet

* but should match the use cases in the datasheet.

*

* In order of power efficiency (least efficient at top).

*

* Mode Description

* FAST Regulator can handle fast changes in it's load.

* e.g. useful in CPU voltage & frequency scaling where

* load can quickly increase with CPU frequency increases.

*

* NORMAL Normal regulator power supply mode. Most drivers will

* use this mode.

*

* IDLE Regulator runs in a more efficient mode for light

* loads. Can be used for devices that have a low power

* requirement during periods of inactivity. This mode

* may be more noisy than NORMAL and may not be able

* to handle fast load switching.

*

* STANDBY Regulator runs in the most efficient mode for very

* light loads. Can be used by devices when they are

* in a sleep/standby state. This mode is likely to be

* the most noisy and may not be able to handle fast load

* switching.

*/

Thanks in advance

Stefan

[igorpadykov]

Hi Stefan

1. seems this is Normal, Idle

2. I think yes

3. one can look at bit LOW_PWR, HW_POWER_REFCTRL

4. suugest to look at attached Linux Manual Chapter 8

i.MX28 Static Power Management Driver

Best regards

igor

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[lategoodbye]

Hi Igor,

i just notice that my questions are a little bit imprecise.

2. Does DISABLE_STEPPING has an influence on efficiency / power consumption of the regulators?

3. Thanks for the hint. But i think more about HW_POWER_5VCTRL, HW_POWER_MINPWR, HW_POWER_VDDDCTRL, HW_POWER_VDDACTRL, HW_POWER_VDDIOCTRL). Are there any helpful settings to influence efficiency?

4. I looked at the original powermanagement driver. Unfortunately the driver doesn't care much about idle / standby state of DC-DC / LINREG.

5. What is recommended state of ENABLE_DCDC for standby state in case of a 5V only setup?

Best regards

Stefan

[igorpadykov · Accepted solution]

Hi Stefan

2. no

3. these settings are very special, as affect accuracy (disable reference circuits)

and brownouts, seems one needs to carefully check if they can be used in every

particular use case

4. I am afraid there is no much else what could be improved compared with

exisiting codes in BSP.

5. in general manupulation with DC-DC configuration may cause power noise, which

may lead to brownout exception. For turning on DC-DC there is erratum 5837.

Once disabled, it may take more time to enable it again, so exit time from

standby state may be increased. So for standby state, it may be recommended

not to change state ENABLE_DCDC.

Best regards

igor