Controlling device power management from terminal

Controlling device power management from terminal

[Crt Mori]

Hi,
I am implementing the power saving modes for mlx90632 device driver
and while I have implemented routines for SET_RUNTIME_PM_OPS
(runtime_pm_suspend and runtime_pm_resume) I am not able to find out
how to trigger them from the terminal.

It could be that my driver code for power management implementation is
incomplete and I need to initialize something more.

Maybe it is helpful, but the power submodule of the device contains below files:

$ ls -al /sys/bus/iio/devices/iio\:device0/power
total 0
drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
-rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
-rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
-rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
-r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage

And control is already set to "auto" which according to documentation
should allow the PM.

Thanks for the hints.

Best regards,
Crt Mori

Re: Controlling device power management from terminal

[Andy Shevchenko]

On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:
>
> Hi,
> I am implementing the power saving modes for mlx90632 device driver
> and while I have implemented routines for SET_RUNTIME_PM_OPS
> (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> how to trigger them from the terminal.
>
> It could be that my driver code for power management implementation is
> incomplete and I need to initialize something more.
>
> Maybe it is helpful, but the power submodule of the device contains below files:
>
> $ ls -al /sys/bus/iio/devices/iio\:device0/power
> total 0
> drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
>
> And control is already set to "auto" which according to documentation
> should allow the PM.

'auto' should enable it. So, whenever the driver thinks it's a time to
power off/on the device it will call the methods.

You may hack a bit to enable autosuspend (which often is not a good
idea for IIO sensors) and see it done automatically after some time.

-- 
With Best Regards,
Andy Shevchenko

Re: Controlling device power management from terminal

[Crt Mori]

On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
>
> On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:
> >
> > Hi,
> > I am implementing the power saving modes for mlx90632 device driver
> > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > how to trigger them from the terminal.
> >
> > It could be that my driver code for power management implementation is
> > incomplete and I need to initialize something more.
> >
> > Maybe it is helpful, but the power submodule of the device contains below files:
> >
> > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > total 0
> > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> >
> > And control is already set to "auto" which according to documentation
> > should allow the PM.
>
> 'auto' should enable it. So, whenever the driver thinks it's a time to
> power off/on the device it will call the methods.
>
> You may hack a bit to enable autosuspend (which often is not a good
> idea for IIO sensors) and see it done automatically after some time.

So the idea is to wait? How would I enable autosuspend - by lowering
the autosusped_delay_ms? How does the driver decide that it is time to
power off/on?

Do I need something else enabled to have this done automatically?
Autosuspend is 5000 in my case which would mean 5 seconds, so I am
quite sure I waited that long and I did not see printk's from the
driver.


>
> --
> With Best Regards,
> Andy Shevchenko

Re: Controlling device power management from terminal

[Andy Shevchenko]

On Mon, Jul 25, 2022 at 11:36 PM Crt Mori <cmo@melexis.com> wrote:
> On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:
> > >
> > > Hi,
> > > I am implementing the power saving modes for mlx90632 device driver
> > > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > > how to trigger them from the terminal.
> > >
> > > It could be that my driver code for power management implementation is
> > > incomplete and I need to initialize something more.
> > >
> > > Maybe it is helpful, but the power submodule of the device contains below files:
> > >
> > > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > > total 0
> > > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> > >
> > > And control is already set to "auto" which according to documentation
> > > should allow the PM.
> >
> > 'auto' should enable it. So, whenever the driver thinks it's a time to
> > power off/on the device it will call the methods.
> >
> > You may hack a bit to enable autosuspend (which often is not a good
> > idea for IIO sensors) and see it done automatically after some time.
>
> So the idea is to wait?

Yes.

> How would I enable autosuspend - by lowering
> the autosusped_delay_ms?

Yep, if you wish. The driver should enable it though.

> How does the driver decide that it is time to
> power off/on?

I'm not a driver author, it seems you , who should answer this
question (as you are about to add PM there, am I right?).

> Do I need something else enabled to have this done automatically?
> Autosuspend is 5000 in my case which would mean 5 seconds, so I am
> quite sure I waited that long and I did not see printk's from the
> driver.

Something prevents it from doing (reference counting) or simply some
initialization / enablement is forgotten. For different buses
different PM runtime rules are applied (for example, IIRC, PCI core
does it for you, while platform bus is on what driver wants basis).

-- 
With Best Regards,
Andy Shevchenko

Re: Controlling device power management from terminal

[Crt Mori]

Hi Andy,
Thanks for the explanation and help - now the PM runtime suspend and
resume are triggered. It was indeed the combination of bad
initialization and that I did not have "enter wakeup" on the read
data.

Currently, I view pm_runtime mode as a power saving mode (device
should be in low power) and normal running as running mode. However,
the sensor is able to report data in both modes - just reading is a
bit different. I also do not have a problem with autosuspend after
some time, but I do wonder how would user change the power mode from
pm_runtime to normal mode (reading, in this case, should not change
the mode). What is the recommended ABI for that?

On Mon, 25 Jul 2022 at 23:45, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
>
> On Mon, Jul 25, 2022 at 11:36 PM Crt Mori <cmo@melexis.com> wrote:
> > On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > > On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:
> > > >
> > > > Hi,
> > > > I am implementing the power saving modes for mlx90632 device driver
> > > > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > > > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > > > how to trigger them from the terminal.
> > > >
> > > > It could be that my driver code for power management implementation is
> > > > incomplete and I need to initialize something more.
> > > >
> > > > Maybe it is helpful, but the power submodule of the device contains below files:
> > > >
> > > > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > > > total 0
> > > > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > > > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> > > >
> > > > And control is already set to "auto" which according to documentation
> > > > should allow the PM.
> > >
> > > 'auto' should enable it. So, whenever the driver thinks it's a time to
> > > power off/on the device it will call the methods.
> > >
> > > You may hack a bit to enable autosuspend (which often is not a good
> > > idea for IIO sensors) and see it done automatically after some time.
> >
> > So the idea is to wait?
>
> Yes.
>
> > How would I enable autosuspend - by lowering
> > the autosusped_delay_ms?
>
> Yep, if you wish. The driver should enable it though.

Is there a way for driver to attach a callback to
power/autosuspend_delay_ms request or to power/control?

>
> > How does the driver decide that it is time to
> > power off/on?
>
> I'm not a driver author, it seems you , who should answer this
> question (as you are about to add PM there, am I right?).
>
> > Do I need something else enabled to have this done automatically?
> > Autosuspend is 5000 in my case which would mean 5 seconds, so I am
> > quite sure I waited that long and I did not see printk's from the
> > driver.
>
> Something prevents it from doing (reference counting) or simply some
> initialization / enablement is forgotten. For different buses
> different PM runtime rules are applied (for example, IIRC, PCI core
> does it for you, while platform bus is on what driver wants basis).
>
> --
> With Best Regards,
> Andy Shevchenko

Re: Controlling device power management from terminal

[Jonathan Cameron]

On Tue, 2 Aug 2022 17:32:22 +0200
Crt Mori <cmo@melexis.com> wrote:

> Hi Andy,
> Thanks for the explanation and help - now the PM runtime suspend and
> resume are triggered. It was indeed the combination of bad
> initialization and that I did not have "enter wakeup" on the read
> data.
> 
> Currently, I view pm_runtime mode as a power saving mode (device
> should be in low power) and normal running as running mode. However,
> the sensor is able to report data in both modes - just reading is a
> bit different. I also do not have a problem with autosuspend after
> some time, but I do wonder how would user change the power mode from
> pm_runtime to normal mode (reading, in this case, should not change
> the mode). What is the recommended ABI for that?

This comes up from time to time.  Normally it's very hard for a user
to know the right answer to power mode questions because they rarely
know enough of the impacts, so we try to use things that do have obvious
meaning.

* If we are doing buffered capture, can assume the user wants good perf
  so switch to a high power mode.  If doing sysfs reads they probably
  care less about perf.  We could apply a heuristic along the lines of
  they read it twice in the last second, keep it in high power mode.

* Often power modes are reflected in sampling rate.  So just wire it up
  to that (with possible side effects on other parameters). 
  I took a quick look at the mlx90632 data sheet and it seems the modes
  we have are.

Sleep step mode:  Goes to sleep between individual measurement sets. So
each one has higher latency after request.  Various subtle complexities
around control int his mode, but it's the latency at start and finish
which differs from other modes

Step mode: Stays powered up, but you need to poll to get a measurement.

Continuous: Autonomous sampling mode.

So fun device. I think you kind of have to implement a heuristic for this.
Probably switch between step mode and sleep step mode based on time between
last two accesses or similar.  If there haven't been 2 accesses yet
stay in sleep step mode.

Side note. As you presumably have hardware for this part, could you run
a rest with UNIVERSAL_DEV_PM_OPS (which is deprecated) switched to
DEFINE_RUNTIME_PM_OPS()  The RUNTIME version checks if we are already
suspended on entry into a full suspend and only powers down the device
if not already powered down.  I plan to spin a patch soon to do this
anyway, but it is technically different behaviour so want it tested
if at all possible! (feel free to not wait for my patch, or to send
your own :)

Jonathan


> 
> On Mon, 25 Jul 2022 at 23:45, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> >
> > On Mon, Jul 25, 2022 at 11:36 PM Crt Mori <cmo@melexis.com> wrote:  
> > > On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:  
> > > > On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:  
> > > > >
> > > > > Hi,
> > > > > I am implementing the power saving modes for mlx90632 device driver
> > > > > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > > > > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > > > > how to trigger them from the terminal.
> > > > >
> > > > > It could be that my driver code for power management implementation is
> > > > > incomplete and I need to initialize something more.
> > > > >
> > > > > Maybe it is helpful, but the power submodule of the device contains below files:
> > > > >
> > > > > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > > > > total 0
> > > > > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > > > > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> > > > >
> > > > > And control is already set to "auto" which according to documentation
> > > > > should allow the PM.  
> > > >
> > > > 'auto' should enable it. So, whenever the driver thinks it's a time to
> > > > power off/on the device it will call the methods.
> > > >
> > > > You may hack a bit to enable autosuspend (which often is not a good
> > > > idea for IIO sensors) and see it done automatically after some time.  
> > >
> > > So the idea is to wait?  
> >
> > Yes.
> >  
> > > How would I enable autosuspend - by lowering
> > > the autosusped_delay_ms?  
> >
> > Yep, if you wish. The driver should enable it though.  
> 
> Is there a way for driver to attach a callback to
> power/autosuspend_delay_ms request or to power/control?
> 
> >  
> > > How does the driver decide that it is time to
> > > power off/on?  
> >
> > I'm not a driver author, it seems you , who should answer this
> > question (as you are about to add PM there, am I right?).
> >  
> > > Do I need something else enabled to have this done automatically?
> > > Autosuspend is 5000 in my case which would mean 5 seconds, so I am
> > > quite sure I waited that long and I did not see printk's from the
> > > driver.  
> >
> > Something prevents it from doing (reference counting) or simply some
> > initialization / enablement is forgotten. For different buses
> > different PM runtime rules are applied (for example, IIRC, PCI core
> > does it for you, while platform bus is on what driver wants basis).
> >
> > --
> > With Best Regards,
> > Andy Shevchenko  

Re: Controlling device power management from terminal

[Crt Mori]

On Sat, 6 Aug 2022 at 19:18, Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Tue, 2 Aug 2022 17:32:22 +0200
> Crt Mori <cmo@melexis.com> wrote:
>
> > Hi Andy,
> > Thanks for the explanation and help - now the PM runtime suspend and
> > resume are triggered. It was indeed the combination of bad
> > initialization and that I did not have "enter wakeup" on the read
> > data.
> >
> > Currently, I view pm_runtime mode as a power saving mode (device
> > should be in low power) and normal running as running mode. However,
> > the sensor is able to report data in both modes - just reading is a
> > bit different. I also do not have a problem with autosuspend after
> > some time, but I do wonder how would user change the power mode from
> > pm_runtime to normal mode (reading, in this case, should not change
> > the mode). What is the recommended ABI for that?
>
> This comes up from time to time.  Normally it's very hard for a user
> to know the right answer to power mode questions because they rarely
> know enough of the impacts, so we try to use things that do have obvious
> meaning.
>
> * If we are doing buffered capture, can assume the user wants good perf
>   so switch to a high power mode.  If doing sysfs reads they probably
>   care less about perf.  We could apply a heuristic along the lines of
>   they read it twice in the last second, keep it in high power mode.
>
I do not think the buffered mode is kinda something that would be
applicable here since refresh rate is not really that fast. (64 Hz).
Or you think I should implement this simply for continuous mode?

> * Often power modes are reflected in sampling rate.  So just wire it up
>   to that (with possible side effects on other parameters).
>   I took a quick look at the mlx90632 data sheet and it seems the modes
>   we have are.
>
> Sleep step mode:  Goes to sleep between individual measurement sets. So
> each one has higher latency after request.  Various subtle complexities
> around control int his mode, but it's the latency at start and finish
> which differs from other modes
This is the new part of the driver I want to add. We call it Burst
measurement mode, and it allows sensor to be in sleep step mode, while
performing triggered measurements. This is the mode I would go after
autosuspend.

>
> Step mode: Stays powered up, but you need to poll to get a measurement.
This mode I would skip. There is no bigger added value at least in Linux case.

>
> Continuous: Autonomous sampling mode.
>
> So fun device. I think you kind of have to implement a heuristic for this.
> Probably switch between step mode and sleep step mode based on time between
> last two accesses or similar.  If there haven't been 2 accesses yet
> stay in sleep step mode.
This mode I would have in repeated measurements. However, how do I
define that? Is there a PM function that would tell me to switch from
Sleep step mode to this? Because runtime_resume in this case would
prevent sensor to work in sleep step mode, so like you suggested I
will check for the time between last two accesses. Does this time need
to be configurable, or can I hardcode it to some "reasonable" value?

>
> Side note. As you presumably have hardware for this part, could you run
> a rest with UNIVERSAL_DEV_PM_OPS (which is deprecated) switched to
> DEFINE_RUNTIME_PM_OPS()  The RUNTIME version checks if we are already
> suspended on entry into a full suspend and only powers down the device
> if not already powered down.  I plan to spin a patch soon to do this
> anyway, but it is technically different behaviour so want it tested
> if at all possible! (feel free to not wait for my patch, or to send
> your own :)
>
I see you already sent your patch, although what I am preparing (with
runtime_pm) will probably overwrite it. I will test your patch
tomorrow as my patches will probably take some time.

Thanks for the answers.
Crt
> Jonathan
>
>
> >
> > On Mon, 25 Jul 2022 at 23:45, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > >
> > > On Mon, Jul 25, 2022 at 11:36 PM Crt Mori <cmo@melexis.com> wrote:
> > > > On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > > > > On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:
> > > > > >
> > > > > > Hi,
> > > > > > I am implementing the power saving modes for mlx90632 device driver
> > > > > > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > > > > > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > > > > > how to trigger them from the terminal.
> > > > > >
> > > > > > It could be that my driver code for power management implementation is
> > > > > > incomplete and I need to initialize something more.
> > > > > >
> > > > > > Maybe it is helpful, but the power submodule of the device contains below files:
> > > > > >
> > > > > > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > > > > > total 0
> > > > > > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > > > > > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> > > > > >
> > > > > > And control is already set to "auto" which according to documentation
> > > > > > should allow the PM.
> > > > >
> > > > > 'auto' should enable it. So, whenever the driver thinks it's a time to
> > > > > power off/on the device it will call the methods.
> > > > >
> > > > > You may hack a bit to enable autosuspend (which often is not a good
> > > > > idea for IIO sensors) and see it done automatically after some time.
> > > >
> > > > So the idea is to wait?
> > >
> > > Yes.
> > >
> > > > How would I enable autosuspend - by lowering
> > > > the autosusped_delay_ms?
> > >
> > > Yep, if you wish. The driver should enable it though.
> >
> > Is there a way for driver to attach a callback to
> > power/autosuspend_delay_ms request or to power/control?
> >
> > >
> > > > How does the driver decide that it is time to
> > > > power off/on?
> > >
> > > I'm not a driver author, it seems you , who should answer this
> > > question (as you are about to add PM there, am I right?).
> > >
> > > > Do I need something else enabled to have this done automatically?
> > > > Autosuspend is 5000 in my case which would mean 5 seconds, so I am
> > > > quite sure I waited that long and I did not see printk's from the
> > > > driver.
> > >
> > > Something prevents it from doing (reference counting) or simply some
> > > initialization / enablement is forgotten. For different buses
> > > different PM runtime rules are applied (for example, IIRC, PCI core
> > > does it for you, while platform bus is on what driver wants basis).
> > >
> > > --
> > > With Best Regards,
> > > Andy Shevchenko
>

Re: Controlling device power management from terminal

[Jonathan Cameron]

On Sun, 7 Aug 2022 23:44:50 +0200
Crt Mori <cmo@melexis.com> wrote:

> On Sat, 6 Aug 2022 at 19:18, Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Tue, 2 Aug 2022 17:32:22 +0200
> > Crt Mori <cmo@melexis.com> wrote:
> >  
> > > Hi Andy,
> > > Thanks for the explanation and help - now the PM runtime suspend and
> > > resume are triggered. It was indeed the combination of bad
> > > initialization and that I did not have "enter wakeup" on the read
> > > data.
> > >
> > > Currently, I view pm_runtime mode as a power saving mode (device
> > > should be in low power) and normal running as running mode. However,
> > > the sensor is able to report data in both modes - just reading is a
> > > bit different. I also do not have a problem with autosuspend after
> > > some time, but I do wonder how would user change the power mode from
> > > pm_runtime to normal mode (reading, in this case, should not change
> > > the mode). What is the recommended ABI for that?  
> >
> > This comes up from time to time.  Normally it's very hard for a user
> > to know the right answer to power mode questions because they rarely
> > know enough of the impacts, so we try to use things that do have obvious
> > meaning.
> >
> > * If we are doing buffered capture, can assume the user wants good perf
> >   so switch to a high power mode.  If doing sysfs reads they probably
> >   care less about perf.  We could apply a heuristic along the lines of
> >   they read it twice in the last second, keep it in high power mode.
> >  
> I do not think the buffered mode is kinda something that would be
> applicable here since refresh rate is not really that fast. (64 Hz).
> Or you think I should implement this simply for continuous mode?

Possibly not. Assuming the non continuous mode is reasonably low latency
I would probably just not implement it.  Maybe it doesn't make any real
sense for this device on Linux.  If latency is quite high you might
make this the 'non autosuspended' case.

> 
> > * Often power modes are reflected in sampling rate.  So just wire it up
> >   to that (with possible side effects on other parameters).
> >   I took a quick look at the mlx90632 data sheet and it seems the modes
> >   we have are.
> >
> > Sleep step mode:  Goes to sleep between individual measurement sets. So
> > each one has higher latency after request.  Various subtle complexities
> > around control int his mode, but it's the latency at start and finish
> > which differs from other modes  
> This is the new part of the driver I want to add. We call it Burst
> measurement mode, and it allows sensor to be in sleep step mode, while
> performing triggered measurements. This is the mode I would go after
> autosuspend.

Sounds reasonable to me.

> 
> >
> > Step mode: Stays powered up, but you need to poll to get a measurement.  
> This mode I would skip. There is no bigger added value at least in Linux case.
> 
> >
> > Continuous: Autonomous sampling mode.
> >
> > So fun device. I think you kind of have to implement a heuristic for this.
> > Probably switch between step mode and sleep step mode based on time between
> > last two accesses or similar.  If there haven't been 2 accesses yet
> > stay in sleep step mode.  
> This mode I would have in repeated measurements. However, how do I
> define that? Is there a PM function that would tell me to switch from
> Sleep step mode to this?

I don't think there is anything appropriate for this.  You can probably
implement it in driver, using some of the ideas from PM.

> Because runtime_resume in this case would
> prevent sensor to work in sleep step mode, so like you suggested I
> will check for the time between last two accesses. Does this time need
> to be configurable, or can I hardcode it to some "reasonable" value?

I'd go for hard coded initially.  If it turns out there is a strong
reason to vary it then we can possibly add that later - though at the
cost of having an interface no one would generally know how to use.

Note the autosuspend delays (which are kind of similar) are almost always
hard coded and we haven't seen much demand to change that.

> 
> >
> > Side note. As you presumably have hardware for this part, could you run
> > a rest with UNIVERSAL_DEV_PM_OPS (which is deprecated) switched to
> > DEFINE_RUNTIME_PM_OPS()  The RUNTIME version checks if we are already
> > suspended on entry into a full suspend and only powers down the device
> > if not already powered down.  I plan to spin a patch soon to do this
> > anyway, but it is technically different behaviour so want it tested
> > if at all possible! (feel free to not wait for my patch, or to send
> > your own :)
> >  
> I see you already sent your patch, although what I am preparing (with
> runtime_pm) will probably overwrite it. I will test your patch
> tomorrow as my patches will probably take some time.

Thanks.

Jonathan

> 
> Thanks for the answers.
> Crt
> > Jonathan
> >
> >  
> > >
> > > On Mon, 25 Jul 2022 at 23:45, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:  
> > > >
> > > > On Mon, Jul 25, 2022 at 11:36 PM Crt Mori <cmo@melexis.com> wrote:  
> > > > > On Mon, 25 Jul 2022 at 23:27, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:  
> > > > > > On Mon, Jul 25, 2022 at 10:48 AM Crt Mori <cmo@melexis.com> wrote:  
> > > > > > >
> > > > > > > Hi,
> > > > > > > I am implementing the power saving modes for mlx90632 device driver
> > > > > > > and while I have implemented routines for SET_RUNTIME_PM_OPS
> > > > > > > (runtime_pm_suspend and runtime_pm_resume) I am not able to find out
> > > > > > > how to trigger them from the terminal.
> > > > > > >
> > > > > > > It could be that my driver code for power management implementation is
> > > > > > > incomplete and I need to initialize something more.
> > > > > > >
> > > > > > > Maybe it is helpful, but the power submodule of the device contains below files:
> > > > > > >
> > > > > > > $ ls -al /sys/bus/iio/devices/iio\:device0/power
> > > > > > > total 0
> > > > > > > drwxrwxr-x 2 root gpio    0 Apr  6 14:17 .
> > > > > > > drwxrwxr-x 3 root gpio    0 Apr  6 14:17 ..
> > > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 async
> > > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:17 autosuspend_delay_ms
> > > > > > > -rw-rw-r-- 1 root gpio 4096 Apr  6 14:18 control
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_kids
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_active_time
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_enabled
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_status
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_suspended_time
> > > > > > > -r--r--r-- 1 root gpio 4096 Apr  6 14:17 runtime_usage
> > > > > > >
> > > > > > > And control is already set to "auto" which according to documentation
> > > > > > > should allow the PM.  
> > > > > >
> > > > > > 'auto' should enable it. So, whenever the driver thinks it's a time to
> > > > > > power off/on the device it will call the methods.
> > > > > >
> > > > > > You may hack a bit to enable autosuspend (which often is not a good
> > > > > > idea for IIO sensors) and see it done automatically after some time.  
> > > > >
> > > > > So the idea is to wait?  
> > > >
> > > > Yes.
> > > >  
> > > > > How would I enable autosuspend - by lowering
> > > > > the autosusped_delay_ms?  
> > > >
> > > > Yep, if you wish. The driver should enable it though.  
> > >
> > > Is there a way for driver to attach a callback to
> > > power/autosuspend_delay_ms request or to power/control?
> > >  
> > > >  
> > > > > How does the driver decide that it is time to
> > > > > power off/on?  
> > > >
> > > > I'm not a driver author, it seems you , who should answer this
> > > > question (as you are about to add PM there, am I right?).
> > > >  
> > > > > Do I need something else enabled to have this done automatically?
> > > > > Autosuspend is 5000 in my case which would mean 5 seconds, so I am
> > > > > quite sure I waited that long and I did not see printk's from the
> > > > > driver.  
> > > >
> > > > Something prevents it from doing (reference counting) or simply some
> > > > initialization / enablement is forgotten. For different buses
> > > > different PM runtime rules are applied (for example, IIRC, PCI core
> > > > does it for you, while platform bus is on what driver wants basis).
> > > >
> > > > --
> > > > With Best Regards,
> > > > Andy Shevchenko  
> >