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

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Date: Fri, 28 Jun 2024 15:56:04 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org, 
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal/core: Introduce user trip points

On Thu, Jun 27, 2024 at 10:55 AM Daniel Lezcano
<daniel.lezcano@...aro.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@...aro.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.

> +
>         /* lower default 0, upper default max_state */
>         lower = lower == THERMAL_NO_LIMIT ? 0 : lower;
>
> diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
> index aa34b6e82e26..f6daf921a136 100644
> --- a/drivers/thermal/thermal_of.c
> +++ b/drivers/thermal/thermal_of.c
> @@ -60,6 +60,7 @@ static const char * const trip_types[] = {
>         [THERMAL_TRIP_PASSIVE]  = "passive",
>         [THERMAL_TRIP_HOT]      = "hot",
>         [THERMAL_TRIP_CRITICAL] = "critical",
> +       [THERMAL_TRIP_USER]     = "user",
>  };
>
>  /**
> diff --git a/drivers/thermal/thermal_trace.h b/drivers/thermal/thermal_trace.h
> index df8f4edd6068..739228ecc2e2 100644
> --- a/drivers/thermal/thermal_trace.h
> +++ b/drivers/thermal/thermal_trace.h
> @@ -15,13 +15,15 @@ TRACE_DEFINE_ENUM(THERMAL_TRIP_CRITICAL);
>  TRACE_DEFINE_ENUM(THERMAL_TRIP_HOT);
>  TRACE_DEFINE_ENUM(THERMAL_TRIP_PASSIVE);
>  TRACE_DEFINE_ENUM(THERMAL_TRIP_ACTIVE);
> +TRACE_DEFINE_ENUM(THERMAL_TRIP_USER);
>
>  #define show_tzt_type(type)                                    \
>         __print_symbolic(type,                                  \
>                          { THERMAL_TRIP_CRITICAL, "CRITICAL"},  \
>                          { THERMAL_TRIP_HOT,      "HOT"},       \
>                          { THERMAL_TRIP_PASSIVE,  "PASSIVE"},   \
> -                        { THERMAL_TRIP_ACTIVE,   "ACTIVE"})
> +                        { THERMAL_TRIP_ACTIVE,   "ACTIVE"}),   \
> +                        { THERMAL_TRIP_USER,     "USER"})
>
>  TRACE_EVENT(thermal_temperature,
>
> diff --git a/drivers/thermal/thermal_trip.c b/drivers/thermal/thermal_trip.c
> index 2a876d3b93aa..a0780bb4ff0d 100644
> --- a/drivers/thermal/thermal_trip.c
> +++ b/drivers/thermal/thermal_trip.c
> @@ -10,6 +10,7 @@
>  #include "thermal_core.h"
>
>  static const char *trip_type_names[] = {
> +       [THERMAL_TRIP_USER] = "user",
>         [THERMAL_TRIP_ACTIVE] = "active",
>         [THERMAL_TRIP_PASSIVE] = "passive",
>         [THERMAL_TRIP_HOT] = "hot",
> diff --git a/include/uapi/linux/thermal.h b/include/uapi/linux/thermal.h
> index fc78bf3aead7..84e556ace5f5 100644
> --- a/include/uapi/linux/thermal.h
> +++ b/include/uapi/linux/thermal.h
> @@ -14,6 +14,7 @@ enum thermal_trip_type {
>         THERMAL_TRIP_PASSIVE,
>         THERMAL_TRIP_HOT,
>         THERMAL_TRIP_CRITICAL,
> +       THERMAL_TRIP_USER,
>  };
>
>  /* Adding event notification support elements */
> --
> 2.43.0
>