On Fri, 22 May 2009, Robert Jarzmik wrote: > Guennadi Liakhovetski <g.liakhovetski@xxxxxx> writes: > > >> Usual question: why do you need an init and halt? What do they do? > > > > Hm, maybe you're right, I don't need them. init() was used in soc_camera > > drivers on first open() to possibly reset the chip and put it in some > > reasonably pre-defined low-power state. But we can do this at the end of > > probe(), which even would be more correct, because even the first open > > should not change chip's configuration. And halt() (was called release() > > originally) is called on last close(). And it seems you shouldn't really > > do this at all - the chip should preserve its configuration between > > open/close cycles. Am I right? > > > > Does anyone among cc'ed authors have any objections against this change? The > > actual disable should indeed migrate to some PM functions, if implemented. > If I understand correctly, what was done before was that on last close, the > sensor was disabled (through sensor->release() call). What will be done now is > leave the sensor on. > > On an embedded system, the power eaten by an active sensor is usually too much > compared to the other components. > > So, if there is a solution which enables, on last close, to power down the > device (or put it in low power mode), in the new API, I'm OK, even if it's a new > powersaving function. If there is no such function and there will be a gap > (let's say kernel 2.6.31 to 2.6.35) where the sensor will be left activated all > the time, then I'm against. > > Let me be even more precise about a usecase : > - a user takes a picture with his smartphone > - the same user then uses his phone to call his girlfriend > - the girlfriend has a lot of things to say, it lasts for 1 hour > In that case, the sensor _has_ to be switched off. Nice example, thanks! Ok, of course, we must not leave the poor girl with her boyfriend's flat battery:-) I think we can put the camera to a low-power state in streamoff. But - not power it off! This has to be done from system's PM functions. What was there on linux-pm about managing power of single devices?... Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
