On Wed, Apr 20, 2022 at 06:58:32AM -0700, Guenter Roeck wrote: > On 4/20/22 06:21, Laurent Pinchart wrote: > > On Wed, Apr 20, 2022 at 03:01:18PM +0200, Benjamin Mugnier wrote: > >> On 20/04/2022 00:04, Guenter Roeck wrote: > >>> On 4/19/22 14:01, Laurent Pinchart wrote: > >>>> On Tue, Apr 19, 2022 at 12:28:06PM -0700, Guenter Roeck wrote: > >>>>> On 4/19/22 11:24, Nicolas Dufresne wrote: > >>>>>> Hi, > >>>>>> > >>>>>> adding linux-hwmon in CC for a wider feedback. > >>>>>> > >>>>>> Le vendredi 15 avril 2022 à 13:18 +0200, Benjamin Mugnier a écrit : > >>>>>>> Add V4L2_CID_TEMPERATURE control to get temperature from sensor in > >>>>>>> celsius as a volatile and read-only control, and its documentation. > >>>>>>> Useful to monitor thermals from v4l controls for sensors that support > >>>>>>> this. > >>>>>> > >>>>>> Any justification to expose a temperature sensor outside of the dedicated kernel > >>>>>> API hwmon ? I know if may makes it harder to use, as the sensor isn't bound to > >>>>>> the camera driver, and also the sensor may not work if the camera is not > >>>>>> streaming. But in the end, the API in hwmon does not look that complex, and is > >>>>>> perhaps more precise ? > >> > >> This sensor is able to read the temperature even if not streaming. > >> > >>>>>> > >>>>>> All in all, I think we need a strong justification to implement a custom > >>>>>> thermometer interface, something described here and documented with care to > >>>>>> prevent abuse. I would also see opinion from folks outside of the linux-media, > >>>>>> hence why I have CCed hwmon mailing list. > >>>>> > >>>>> All I can say is that this seems to be odd and a bit outside the scope of > >>>>> v4l2. I would have expected the vgxy61 driver to register a hwmon device > >>>>> instead. > >>>> > >>>> I don't have a definitive opinion yet, but as Nicolas raised the issue > >>>> by pushing towards hwmon, I'll offer counter-arguments for the sake of > >>>> it :-) > >>>> > >>>> The temperature sensor in the imaging sensor is used to measure the die > >>>> temperature, in order to tune the noise and spectral response model of > >>>> the imaging sensor. It's thus not a generic-purpose temperature sensor. > >>>> If the feature were to be exposed through hwmon, userspace would need to > >>>> associate an hwmon device to the imaging sensor V4L2 subdev (we have a > >>>> way to do so through the MC API, it doesn't support hwmon at this point, > >>>> but I suppose it could be added). There are also various constraints > >>>> that tie the temperature reading to the imaging side, it could be that > >>>> the temperature would only be readable while capturing frames. That's > >>>> probably possible to handle too but returning an error from the > >>>> temperature read. > >>>> > >>>> Code-wise, both the driver and userspace would be more complex, for very > >>>> little practical gain (I don't dispute a theorical gain). > >>>> > >>> > >>> All I can say is - not my subsystem, not my call to make. If you say this > >>> is special and is better handled in V4L2, I'll take you by your word. > >>> > >>> Guenter > >>> > >> > >> I'll happily implement whatever conclusion we make here. > >> > >> I could also drop this control for the first iteration of the driver, > >> and come back later once a consensus is reached. > > > > That would work too. By the way, what are your use cases for the > > temperature sensor ? Have you added the control for the sake of > > completeness, or do you have use cases ? > > You provided a use case above. Are you saying you made it up ? > Still fine with me, your call, just wondering. It's the two most common use cases for imaging sensor temperature measurements that I know of. My question to Benjamin is if he has the same and/or other use cases. -- Regards, Laurent Pinchart
