Messages in this thread | | | Date | Thu, 31 Jul 2014 10:17:17 -0700 | From | Matt Longnecker <> | Subject | Re: [PATCH] thermal: tell cooling devices when a trip_point changes |
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I should have labeled my message RFC. My intent was to generate some public discussion about a problem I've hit -- not to get this particular patch merged.
On 07/31/2014 01:30 AM, Zhang Rui wrote: > On Wed, 2014-07-30 at 16:10 -0700, Matt Longnecker wrote: >> Some hardware can react autonomously at a programmed temperature. > > if you have a temperature sensor, then you should have a thermal zone > device driver for it, right? >
Yes, but....
In existing "downstream" Tegra kernels, thermal sensor drivers directly register thermal zones with thermal_core.c. Drivers get information for the zone (e.g. trip points, cooling maps, etc). Each driver has its own format for this zone-related information.
Now we're moving away from board files and toward device tree.
of-thermal offers a canonical way to encode zone-related information in device tree. I don't want to invent a competing alternative.
As of-thermal parses device tree, it creates thermal zones. Sensor drivers no longer need to register zones -- they just register with of-thermal as sensor drivers.
of-thermal hides trip points and cooling maps from sensor drivers. This is good and bad. It's good because it eliminates a _lot_ of thermal zone boilerplate code from sensor drivers. It's bad because it breaks an existing usecase: * the kernel configures the hardware thermal reaction (e.g. catastrophic shutdown) according to platform-data provided at boot * a user adjusts the shutdown temperature at runtime by poking at /sys/class/thermal/thermal_zone*/trip_point_*_temp
My patch offers one way to support this usecase in systems using of-thermal to manage thermal zones. I'm happy to discuss alternatives.
>> For example, an SoC might implement a last ditch throttle or a >> hardware thermal shutdown. > > And it should be handled by the thermal zone driver, who has the > knowledge of when to do throttle/shutdown. >
of-thermal doesn't support this because it doesn't propagate trip point changes to sensor drivers.
Thanks, Matt Longnecker
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