On Tue, Oct 17, 2017 at 09:03:40PM +0200, Daniel Lezcano wrote: > On 17/10/2017 20:25, Eduardo Valentin wrote: > > Hello, > > > > On Tue, Oct 17, 2017 at 02:28:27PM +0200, Daniel Lezcano wrote: > >> On 17/10/2017 05:54, Eduardo Valentin wrote: > >>> On Tue, Oct 10, 2017 at 08:02:27PM +0200, Daniel Lezcano wrote: > >>>> By essence, the tsensor does not really support multiple sensor at the > >>>> same > >>>> time. It allows to set a sensor and use it to get the temperature, > >>>> another > >>>> sensor could be switched but with a delay of 3-5ms. It is difficult to > >>>> read > >>>> simultaneously several sensors without a big delay. > >>>> > >>> > >>> Is 3-5 ms enough to loose an event? Is this really a problem? > >> > >> There are several aspects: > >> > >> - the multiple sensors is not needed here > > > > Well, that is debatable, I cannot really agree or disagree with the > > above statement without understanding the use cases and most important, > > the location of each sensor. What is the location of each sensor? > > > >> > >> - the temperature controller is not designed to read several sensors at > >> the same time, we switch the sensor and that clears some internal > >> buffers and re-init the controller > > > > Which is still very helpful in case you have multiple hotspots that you > > want to track and they are exposed on different workloads. Sacrificing > > the availability of sensors is something needs a better justification > > other than "current code uses only one". > > > > > >> > >> - some boards can take 40°C in 1 sec, the temperature increase is > >> insanely fast and reading several sensors add an extra 15ms. > >> > > > > > > Ok... What is the difference in update rate with and without the switch > > of sensors? With the above worst case, you have about 4/6 mC/ms. Can > > your tsensor support that resolution for a single sensor? What is the > > maximum resolution a tsensor can support? What is the penalty added with > > switch? > > > > Based on this data, and the above 3-5ms, that means you would miss about > > ~ 3 - 4 mC while switching ( assuming tsensor can really achieve the > > above rate of change: 5ms * 4/6 mC /ms). Are you sure that is > > enough justification to drop three extra sensors? > > Ok if I refer to the documentation the rate is 0.768 ms with the current > configuration. > > The driver is currently bogus: register overwritten, bouncing interrupt, > unneeded lock, ... So the proposition was to remove the multiple sensors > support, clean the driver, and re-introduce it if there is a need. > > If I remember correctly Leo, author of the driver, agreed on this. Leo ? > > Note, I'm not strongly against multiple sensors support in the driver if > you think it is convenient but it is much simpler to remove the current > code as it is not used and put it back on top of a sane foundation > instead of circumventing that on the existing code. > >
I am also fine with the above strategy, as long as you are sure you are not breaking anyone (specially userspace). Also, it would be good to get a reviewed-by from hisilicon just to confirm (Leo?). Besides, once you get his reviewed-by, and add it to the patches, can you please resend the series with the minor issues I mentioned (a few minor checkpatch issues and one compilation warn that is added to the driver after the series is applied). > > > > -- > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs > > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | > <http://twitter.com/#!/linaroorg> Twitter | > <http://www.linaro.org/linaro-blog/> Blog >
