Re: (bug report) HWMON & Thermal interactions
From: Guenter Roeck
Date: Mon Oct 24 2022 - 11:58:45 EST
On 10/24/22 05:47, Cristian Marussi wrote:
On Mon, Oct 24, 2022 at 04:56:43AM -0700, Guenter Roeck wrote:
On 10/23/22 14:23, Guenter Roeck wrote:
On 10/23/22 11:27, Cristian Marussi wrote:
Hi,
Starting with v6.1-rc1 the SCMI HWMON driver failed probing on my JUNO due
to the fact that no trip points were (ever !) defined in the DT; bisecting it
looks like that after:
https://lore.kernel.org/all/20220804224349.1926752-28-daniel.lezcano@xxxxxxxxxx/
the presence of the mandatory trips node within thermal zones is now
enforced.
So, this is NOT what this bug report is about (I'll post soon patches for
the JUNO DT missing trips) BUT once this problem was solved in the DT,
another issue appeared:
[ 1.921929] hwmon hwmon0: temp2_input not attached to any thermal zone
that despite having now a goodi/valid DT describing 2 sensors and 2 thermal zones
embedding that sensors, only the first one is found as belonging to one ThermZ.
(this happens ALSO with v6.0 once I added the trips...)
Digging deep into this, it turned out that inside the call chain
devm_hwmon_device_register_with_info
hwmon_device_register_with_info
__hwmon_device_register
hwmon_thermal_register_sensors(dev)
--> hwmon_thermal_add_sensor(dev, j)
--> devm_thermal_of_zone_register(dev, sensor_id, tdata, )
the HWMON channel index j is passed to the Thermal framework in order to
search and bind sensors with defined thermal zone, but this lead to the
assumption that sequential HWMON channel indexes corresponds one-to-one to the
underlying real sensor IDs that the ThermalFramework uses for matching
within the DT.
On a system like my SCMI-based DT where I have 2 temp-sensors bound to 2
thermal zones like:
thernal_zones {
pmic {
...
thermal-sensors = <&scmi_sensors0 0>;
...
trips {
...
}
soc {
...
thermal-sensors = <&scmi_sensors0 3>;
...
trips {
...
}
}
}
This works fine by chance for the pmic (j=0, sensor_id=0) BUT cannot work for
the soc where J=1 BUT the real sensor ID is 3.
Note that there can be a number of sensors, not all of them of a type handled
by HWMON, and enumerated by SCMI in different ways depending on the
platform.
I suppose this is not an SCMI-only related issue, but maybe in non-SCMI
context, where sensors are purely defined in the DT, the solution can be
more easily attained (i.e. renumber the sensors).
At first I tried to solve this inside scmi-hwmon.c BUT I could not find
a way to present to the HWMON subsystem the list of sensors preserving
the above index/sensor_id matching (not even with a hack like passing
down dummy sensors to the HWMON subsystem to fill the 'holes' in the
numbering)
My tentative solution, which works fine for me in my context, was to add
an optional HWMON hwops, so that the core hwmon can retrieve if needed the
real sensor ID if different from the channel index (using an optional hwops
instead of some static hwinfo var let me avoid to have to patch all the
existent hwmon drivers that happens to just work fine as of today...but
maybe it is not necessarily the proper final solution...)
i.e.
----8<----
Author: Cristian Marussi <cristian.marussi@xxxxxxx>
Date: Fri Oct 21 17:24:04 2022 +0100
hwmon: Add new .get_sensor_id hwops
Add a new optional helper which can be defined to allow an hwmon chip to
provide the logic to map hwmon indexes to the real underlying sensor IDs.
Maybe I am missing something, but ...
The driver isn't supposed to know anything about thermal devices and
thermal zones. If that no longer works, and drivers have to know about
thermal zones and thermal zone device index values anyway, we might
as well pull thermal device support from the hwmon core and implement
it in drivers.
No, wait: The question is really: Why does the scmi driver present the sensor
with index 3 to the hwmon subsystem as sensor with index 1 ?
If the sensor has index 3, and is presented to other entities as sensor
with index 3, it should be presented to the hwmon subsystem as sensor with
index 3, not with index 1. If sensors with index 1..2 do not exist,
the is_visible function should return 0 for those sensors.
My understanding was that the hwmon index is the index of the channel
and hwmon_channel_info struct groups channels by type while the index is
really used as a pointer in the hwmon_channel_info.config field, so in
this case you're saying I should present 4 temp sensors placing a 'hole'
at sensor 1,2 making is_visible return 0 for those channels ?
Basically keeping the channel indexes in sync with the real sensor ID by
the means of some dummy sensor entries in the config field: this could result
potentially in a lot of holes given in SCMI the sensor_id is 16 bits and
I thought that was too hackish but I can try.
The underlying idea with the hwmon -> thermal bridge is that index values
used by thermal and by the hwmon subsystem match and, yes, that there would
if necessary be holes in hwmon index values (normally this is not a 16-bit
number space). If that doesn't work for scmi, and if there could indeed be
something like
thermal-sensors = <&scmi_sensors0 12345>;
then I think the solution is indeed to not rely on the hwmon->thermal bridge
in the hwmon core for this driver.
In the meantime, I gave it a go at what you suggested early (if I got it
right...) by removing from the scmi-hwmon driver the HWMON_C_REGISTER_TZ
attribute and adding a few explicit calls to devm_thermal_of_zone_register() at
the end of the probe to specifically register the needed temp sensors (and
associated real sensor IDs) with the ThermalFramework without relying on the
HWMON core for Thermal and it works fine indeed.
Excellent.
Thanks,
Guenter