On Fri, Mar 24, 2017 at 01:23:13PM +0000, Russell King - ARM Linux wrote:
> On Mon, Mar 20, 2017 at 12:15:52PM -0500, Rob Herring wrote:
> > On Sun, Mar 12, 2017 at 07:07:40PM +0000, Russell King wrote:
> > > Allow hwmon devices to be optionally created for of-thermal zones,
> > > rather than permanently denying them "in case" there is a hwmon
> > > driver duplicating the thermal driver.
> > >
> > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> > > ---
> > > Without this, "sensors" is unable to report the temperature of the
> > > Dove SoC when it supports thermal zones.
> > >
> > > Documentation/devicetree/bindings/thermal/thermal.txt | 3 +++
> > > arch/arm/boot/dts/dove.dtsi | 1 +
> > > drivers/thermal/of-thermal.c | 3 ++-
> > > 3 files changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/thermal/thermal.txt b/Documentation/devicetree/bindings/thermal/thermal.txt
> > > index 88b6ea1ad290..1478735fff85 100644
> > > --- a/Documentation/devicetree/bindings/thermal/thermal.txt
> > > +++ b/Documentation/devicetree/bindings/thermal/thermal.txt
> > > @@ -175,6 +175,9 @@ containing trip nodes and one sub-node containing all the zone cooling maps.
> > > 2000mW, while on a 10'' tablet is around
> > > 4500mW.
> > >
> > > +- linux,hwmon: Allow Linux to create hwmon devices for the thermal
> > > + Type: bool zone.
> > > +
> > > Note: The delay properties are bound to the maximum dT/dt (temperature
> > > derivative over time) in two situations for a thermal zone:
> > > (i) - when passive cooling is activated (polling-delay-passive); and
> > > diff --git a/arch/arm/boot/dts/dove.dtsi b/arch/arm/boot/dts/dove.dtsi
> > > index 40fb98687230..00f5971cd039 100644
> > > --- a/arch/arm/boot/dts/dove.dtsi
> > > +++ b/arch/arm/boot/dts/dove.dtsi
> > > @@ -804,6 +804,7 @@
> > >
> > > thermal-zones {
> > > soc-thermal {
> > > + linux,hwmon;
> >
> > I'd prefer to see a black or white list of sensor compatibles here. Then
> > the dtb doesn't need to change if things move between hwmon and thermal
> > zones.
>
> I'm not sure what you mean, and I can't see how that would be coded up.
> The thermal layer doesn't give the option of individually selecting
> which sensors have hwmon stuff created - it seems to be all or nothing.
> I suspect what you're asking would require something of a rewrite of
> the thermal code. The sensors are registered completely independently
> of parsing the thermal zone data.
Okay, I'm convinced that what you're asking for (if I'm understanding
correctly) is just not possible with how the thermal code is (horribly)
architected at the moment.
While trying to understand how all the thermal zone stuff fits together,
I found this comment:
/* For now, thermal framework supports only 1 sensor per zone */
ret = of_parse_phandle_with_args(child, "thermal-sensors",
"#thermal-sensor-cells",
0, &sensor_specs);
so it's really not setup to deal with multiple sensors in DT right now
(and there's no checking by the code that this is even the case.)
The way the code is architected, the thermal zone devices and hwmon
support is setup _completely_ independently from attaching the single
sensor to the zone - the setup of the thermal zone devices and
registering the sysfs entry happens before the sensors.
The hwmon support is coded such that there is one hwmon device for all
thermal zones. Each thermal zone device exports exactly one hwmon
temperature sensor value with one set of trip points.
A thermal zone device can support multiple sensors, but from the code
and the above comment, the code does not support this - the sensors
are not individually exported through hwmon.
So, I think what you're asking for is not possible and is based upon
a mis-understanding - thermal does not export sensors, but exports the
_zone_ itself as a hwmon sensor. The zone temperature is exported,
along with its thresholds.
Obviously, the separation of thermal vs hwmon is purely a Linux
phenomenon, and I've wondered why people have to rewrite hwmon drivers
as thermal drivers just to make use of the thermal subsystem - it seems
to me like NIH syndrome. I can't see why hwmon isn't able to export
individual temperature sensors to thermal and have thermal import the
values from there.
For example, you could have a hwmon device that has multiple temperature
sensors (some do) which monitor different parts of the system, and a
hwmon device should be able to be incorporated into a thermal zone for
management.
That doesn't seem possible, you have to implement a thermal driver to
interface your sensor to the thermal stuff, and then have the _zone_
statistics exported through hwmon.
If you want individual sensors exported, you have to implement a driver
which has a dual-personality, it has to register with hwmon and thermal.
I'd say that, arguably, the whole "no_hwmon" thing in thermal is also
wrong - it may _seem_ to be correct because thermal only supports one
sensor, and we don't want such a dual-personality driver to have two
entries in sysfs, but that's rather moot when you consider that one is
exporting the zone (which has DT configured thresholds) and one is
exporting the sensor itself.
So, my conclusion is that this is all rather messed up, and certainly
beyond my willingness to put in a lot of effort, creating lots of
patches to try and bring the code to a point where what you're asking
for is possible (iow, where we export individual sensors to hwmon,
and make individual sensors exportable.)
Therefore, I believe that my implementation is entirely reasonable -
the linux,hwmon flag indicates whether the state of the thermal _zone_
(not the _sensors_) should be exported via hwmon.
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