Re: [PATCH] thermal/core: Introduce user trip points

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Jul 1, 2024 at 3:17 PM Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> On 28/06/2024 15:56, Rafael J. Wysocki wrote:
> > On Thu, Jun 27, 2024 at 10:55 AM Daniel Lezcano
> > <daniel.lezcano@linaro.org> wrote:
> >>
> >> Currently the thermal framework has 4 trip point types:
> >>
> >> - active : basically for fans (or anything requiring energy to cool
> >>    down)
> >>
> >> - passive : a performance limiter
> >>
> >> - hot : for a last action before reaching critical
> >>
> >> - critical : a without return threshold leading to a system shutdown
> >>
> >> A thermal zone monitors the temperature regarding these trip
> >> points. The old way to do that is actively polling the temperature
> >> which is very bad for embedded systems, especially mobile and it is
> >> even worse today as we can have more than fifty thermal zones. The
> >> modern way is to rely on the driver to send an interrupt when the trip
> >> points are crossed, so the system can sleep while the temperature
> >> monitoring is offloaded to a dedicated hardware.
> >>
> >> However, the thermal aspect is also managed from userspace to protect
> >> the user, especially tracking down the skin temperature sensor. The
> >> logic is more complex than what we found in the kernel because it
> >> needs multiple sources indicating the thermal situation of the entire
> >> system.
> >>
> >> For this reason it needs to setup trip points at different levels in
> >> order to get informed about what is going on with some thermal zones
> >> when running some specific application.
> >>
> >> For instance, the skin temperature must be limited to 43°C on a long
> >> run but can go to 48°C for 10 minutes, or 60°C for 1 minute.
> >>
> >> The thermal engine must then rely on trip points to monitor those
> >> temperatures. Unfortunately, today there is only 'active' and
> >> 'passive' trip points which has a specific meaning for the kernel, not
> >> the userspace. That leads to hacks in different platforms for mobile
> >> and embedded systems where 'active' trip points are used to send
> >> notification to the userspace. This is obviously not right because
> >> these trip are handled by the kernel.
> >>
> >> This patch introduces the 'user' trip point type where its semantic is
> >> simple: do nothing at the kernel level, just send a notification to
> >> the user space.
> >>
> >> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> >> ---
> >>   .../devicetree/bindings/thermal/thermal-zones.yaml        | 1 +
> >>   drivers/thermal/thermal_core.c                            | 8 ++++++++
> >>   drivers/thermal/thermal_of.c                              | 1 +
> >>   drivers/thermal/thermal_trace.h                           | 4 +++-
> >>   drivers/thermal/thermal_trip.c                            | 1 +
> >>   include/uapi/linux/thermal.h                              | 1 +
> >>   6 files changed, 15 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/thermal/thermal-zones.yaml b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> >> index 68398e7e8655..cb9ea54a192e 100644
> >> --- a/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> >> +++ b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> >> @@ -153,6 +153,7 @@ patternProperties:
> >>                 type:
> >>                   $ref: /schemas/types.yaml#/definitions/string
> >>                   enum:
> >> +                  - user     # enable user notification
> >>                     - active   # enable active cooling e.g. fans
> >>                     - passive  # enable passive cooling e.g. throttling cpu
> >>                     - hot      # send notification to driver
> >> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> >> index 2aa04c46a425..506f880d9aa9 100644
> >> --- a/drivers/thermal/thermal_core.c
> >> +++ b/drivers/thermal/thermal_core.c
> >> @@ -734,6 +734,14 @@ int thermal_bind_cdev_to_trip(struct thermal_zone_device *tz,
> >>          if (tz != pos1 || cdev != pos2)
> >>                  return -EINVAL;
> >>
> >> +       /*
> >> +        * It is not allowed to bind a cooling device with a trip
> >> +        * point user type because no mitigation should happen from
> >> +        * the kernel with these trip points
> >> +        */
> >> +       if (trip->type == THERMAL_TRIP_USER)
> >> +               return -EINVAL;
> >
> > Maybe print a debug message when bailing out here?
> >
> > A check for "user" trips would need to be added to
> > thermal_governor_trip_crossed() and to the .manage() callbacks in the
> > power allocator, step-wise and fair-share governors, if I'm not
> > mistaken.  Especially fair-share and power allocator should not take
> > them into account IMV.
>
> I'm not sure the power_allocator needs to change anything. The trip
> point used is switch_on which is only derived from passive or active
> trip point, so it is not possible to have a user trip point used in the
> manage callback.

OK, it checks for "active" specifically.

> Did I miss something ?

No, I don't think so.