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

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Date: Mon, 1 Jul 2024 15:17:03 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: 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 28/06/2024 15:56, Rafael J. Wysocki wrote:
> 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.

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.

Did I miss something ?


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