[PATCH v1 0/9] thermal: Writable trip points handling rework

[Rafael J. Wysocki]

Hi Everyone,

The purpose of this patch series is to allow thermal zone creators
to specify which properties (temperature or hysteresis) of which
trip points can be set from user space via sysfs on a per-trip basis
instead of passing writable trips masks to the thermal zone registration
function which is both cumbersome and error prone and it doesn't even
allow to request different treatment of different trip properties.

The writable trip masks used today only affect trip temperatures (that is, if
a trip point is in a writable trips mask, its temperature can be set via
sysfs) and they only take effect if the CONFIG_THERMAL_WRITABLE_TRIPS kernel
configuration option is set, which appears to be assumed by at least some
of the drivers using writable trips masks.  Some other drivers using them
simply select CONFIG_THERMAL_WRITABLE_TRIPS which pretty much defeats its
purpose (and imx even sets this option in its defconfig).

For this reasons, patch [1/9] removes CONFIG_THERMAL_WRITABLE_TRIPS and makes
the writable trips masks always work.

Moreover, trip hysteresis, which is not affected either by the writable trips
masks or by CONFIG_THERMAL_WRITABLE_TRIPS, can only be set via sysfs if the
set_trip_hyst() operation is provided by the given thermal zone, but currently
this thermal zone operation is used by no one, so effectively trip hysteresis
cannot be set via sysfs at all.  This is not a problem for the majority of
drivers that want trip temperatures to be set via sysfs, because they also
don't want trip hysteresis to be changed for any trips (at least as far as I
can say), but there are use cases in which it is desirable to be able to
update trip hysteresis as well as trip temperature (for example see
https://lore.kernel.org/linux-pm/20240106191502.29126-1-quic_manafm@xxxxxxxxxxx/).
Those use cases are not addressed here directly, but after this series
addressing them should be relatively straightforward.

Namely, patch [2/9] adds flags to struct thermal_trip and defines two of them
to indicate whether or not setting the temperature or hysteresis of the given
trip via sysfs is allowed.  If a writable trips mask is passed to
thermal_zone_device_register_with_trips(), is it is used to set the
"writable temperature" flag for the trips covered by it and that flag is
then consulted by the thermal sysfs code.  The "writable hysteresis" trip
flag is also taken into account by the thermal sysfs code, but it is not set
automatically in any case.

Patch [3/9] is based on the observation that the .set_trip_hyst() thermal zone
operation is never used - it simply drops that callback from struct
thermal_zone_device_ops and adjusts the code checking its presence.

Patches [4-8/9] update drivers using writable trips masks to set the new
"writable temperature" flag directly instead and some of them are simplified
a bit as a result.  After these patches, all of the callers of
thermal_zone_device_register_with_trips() pass a zero writable trips mask
to it, so patch [9/9] drops that mask from the functions argument list and
adjusts all of its callers accordingly.

After all of the changes in this series, allowing the hysteresis value to be
set via sysfs for a given trip is a matter of setting its "writable
hysteresis" flag (and analogously for trip temperature).

Thanks!