On 30.01.2025 12:07, Daniel Lezcano wrote:

On Thu, Jan 30, 2025 at 11:08:03AM +0200, Claudiu Beznea wrote:

quoted

Hi, Daniel,

On 29.01.2025 19:24, Daniel Lezcano wrote:

quoted

Hi Claudiu,

On Fri, Jan 03, 2025 at 06:38:01PM +0200, Claudiu wrote:

quoted

From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>

On the Renesas RZ/G3S (and other Renesas SoCs, e.g., RZ/G2{L, LC, UL}),
clocks are managed through PM domains. These PM domains, registered on
behalf of the clock controller driver, are configured with
GENPD_FLAG_PM_CLK. In most of the Renesas drivers used by RZ SoCs, the
clocks are enabled/disabled using runtime PM APIs.

During probe, devices are attached to the PM domain controlling their
clocks. Similarly, during removal, devices are detached from the PM domain.

The detachment call stack is as follows:

device_driver_detach() ->
  device_release_driver_internal() ->
    __device_release_driver() ->
      device_remove() ->
        platform_remove() ->
	  dev_pm_domain_detach()

In the upcoming Renesas RZ/G3S thermal driver, the
struct thermal_zone_device_ops::change_mode API is implemented to
start/stop the thermal sensor unit. Register settings are updated within
the change_mode API.

In case devres helpers are used for thermal zone register/unregister the
struct thermal_zone_device_ops::change_mode API is invoked when the
driver is unbound. The identified call stack is as follows:

device_driver_detach() ->
  device_release_driver_internal() ->
    device_unbind_cleanup() ->
      devres_release_all() ->
        devm_thermal_of_zone_release() ->
	  thermal_zone_device_disable() ->
	    thermal_zone_device_set_mode() ->
	      rzg3s_thermal_change_mode()

The device_unbind_cleanup() function is called after the thermal device is
detached from the PM domain (via dev_pm_domain_detach()).

The rzg3s_thermal_change_mode() implementation calls
pm_runtime_resume_and_get()/pm_runtime_put_autosuspend() before/after
accessing the registers. However, during the unbind scenario, the
devm_thermal_of_zone_release() is invoked after dev_pm_domain_detach().
Consequently, the clocks are not enabled, as the device is removed from
the PM domain at this time, leading to an Asynchronous SError Interrupt.
The system cannot be used after this.

I've been through the driver before responding to this change. What is the
benefit of powering down / up (or clock off / on) the thermal sensor when
reading the temperature ?

I can understand for disable / enable but I don't get for the classic usage
where a governor will be reading the temperature regularly.

I tried to be as power saving as possible both at runtime and after the IP
is not used anymore as the HW manual doesn't mentioned anything about
accuracy or implications of disabling the IP clock at runtime. We use
similar approach (of disabling clocks at runtime) for other IPs in the
RZ/G3S SoC as well.

quoted

Would the IP need some cycles to capture the temperature accurately after the
clock is enabled ?

There is nothing about this mentioned about this in the HW manual of the
RZ/G3S SoC. The only points mentioned are as described in the driver code:
- wait at least 3us after each IIO channel read
- wait at least 30us after enabling the sensor
- wait at least 50us after setting OE bit in TSU_SM

For this I chose to have it implemented as proposed.

IMO, disabling/enabling the clock between two reads through the pm runtime may
not be a good thing, especially if the system enters a thermal situation where
it has to mitigate.

Without any testing capturing the temperatures and compare between the always-on
and on/off, it is hard to say if it is true or not. Up to you to test that or
not. If you think it is fine, then let's go with it.

I tested it with and w/o the runtime PM and on/off support (so, everything
ON from the probe) and the reported temperature values were similar.

Thank you,
Claudiu

quoted

If any, the HW manual is available here
https://www.renesas.com/en/document/mah/rzg3s-group-users-manual-hardware?r=25458591
(an archive is here; the manual is in Deliverables/r01uh1014ej0110-rzg3s.pdf)

Thank you for your review,
Claudiu

quoted

quoted

Add thermal_of_zone_register()/thermal_of_zone_unregister(). These will
be used in the upcomming RZ/G3S thermal driver.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>