linux-kernel - Re: [PATCH 1/3] thermal: core: Add indication for userspace usage

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Date:   Mon, 30 Nov 2020 10:39:17 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, amitk@...nel.org,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] thermal: core: Add indication for userspace usage

On Tue, 2020-12-01 at 02:22 +0800, Kai-Heng Feng wrote:
> > On Dec 1, 2020, at 02:13, Srinivas Pandruvada <
> > srinivas.pandruvada@...ux.intel.com> wrote:
> 
> [snipped] 
> 
> > > > What about creating an new callback
> > > > 
> > > > enum thermal_trip_status {
> > > > 	THERMAL_TRIP_DISABLED = 0,
> > > > 	THERMAL_TRIP_ENABLED,
> > > > };
> > > > 
> > > > int get_trip_status(struct thermal_zone_device *, int trip,
> > > > enum
> > > > thermal_trip_status *state);
> > > > 
> > > > Then in 
> > > > static void handle_thermal_trip(struct thermal_zone_device *tz,
> > > > int
> > > > trip)
> > > > {
> > > > 
> > > > /* before tz->ops->get_trip_temp(tz, trip, &trip_temp); */
> > > > if (tz->ops->get_trip_status) {
> > > > 	enum thermal_trip_status *status;
> > > > 
> > > > 	if (!tz->ops->get_trip_status(tz, trip, &status)) {
> > > > 		if (status == THERMAL_TRIP_DISABLED)
> > > > 			return;	
> > > > 	}
> > > > }
> > > > ...
> > > > ...
> > > > 
> > > > }
> > > > 
> > > > 
> > > > This callback will help the cases:
> > > > - Allows drivers to selectively disable certain trips during
> > > > init
> > > > state
> > > > or system resume where there can be spikes or always. int340x
> > > > drivers
> > > > can disable always.
> > > 
> > > This sounds really great. This is indeed can happen on system
> > > resume,
> > > before userspace process thaw.
> > > 
> > > > - Still give options for drivers to handle critical trip even
> > > > if
> > > > they
> > > > are bound to user space governors. User space process may be
> > > > dead,
> > > > so
> > > > still allow kernel to process graceful shutdown
> > > 
> > > To make the scenario happen, do we need a new sysfs to let
> > > usespace
> > > enable it with THERMAL_TRIP_ENABLED?
> > This should be drivers call not user space.
> 
> Understood. So after thermal_zone_device_register(), the driver can
> decide to what to return on get_trip_temp().
get_trip_status()

> Let me work on a new patch if there's no other concern.
Better to wait for confirmation from Daniel and others.

Thanks,
Srinivas

> 
> Kai-Heng
> 
> > Thanks,
> > Srinivas