On Mon, May 18, 2015 at 11:44:33AM -0700, Brian Norris wrote: > On Mon, May 18, 2015 at 02:09:44PM +0200, Sascha Hauer wrote: > > On Mon, May 18, 2015 at 12:06:50PM +0300, Mikko Perttunen wrote: > > > One interesting thing I noticed was that at least the bang-bang > > > governor only acts if the temperature is properly smaller than (trip > > > temp - hysteresis). So perhaps we should specify the non-tripping > > > range as [low, high)? Or we could change bang-bang. > > > > I wonder how we can protect against such off-by-one errors anyway. > > Generally a hardware might operate on raw values rather than directly > > in temperature values in °C. This means a driver for this must have > > celsius_to_raw and raw_to_celsius conversion functions. Now it can > > happen that due to rounding errors celsius_to_raw(Tcrit) returns a raw > > value that when converted back to celsius is different from the > > original value in °C. This would mean the hardware triggers an interrupt > > for a trip point and the thermal core does not react because get_temp > > actually returns a different temperature than previously programmed as > > interrupt trigger. This way we would lose hot (or cold) events. > > This also highlights another fact: there's a race between interrupt > generation and temperature reading (->get_temp()). I would expect any > hardware interrupt thermal sensor would also have a latched temperature > reading to correspond with it, and there would be no guarantee that this > latched temperature will match the polled reading seen once you reach > thermal_zone_device_update(). So a hardware driver might report a > thermal update, but the temperature reported to the core won't > necessarily match what interrupt was meant for. > > I have a patch that adds a thermal_zone_device_update_temp() API, so > drivers can report the temperature along with the interrupt > notification. (Such a patch also helps so that the driver can choose to > round down on cold events and up on hot events, resolving your rounding > issue too.)
Could you send me that patch? Thinking about it this might indeed work. The only thing that a driver needs to make sure then is that it actually at least one time reports a temperature beyond the currently programmed thresholds. With the patch you describe a driver could simply do that by ignoring the current ADC values and simply reporting the previously desired values. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
