On Sun, 27 Feb 2011, Sakari Ailus wrote: > Hi, > > Guennadi Liakhovetski wrote: > > On Fri, 25 Feb 2011, Sakari Ailus wrote: > > > > > Hi Guennadi, > > > > > > Guennadi Liakhovetski wrote: > > > > In principle - yes, and yes, I do realise, that the couple of controls, > > > > that I've proposed only cover a very minor subset of the whole flash > > > > function palette. The purposes of my RFC were: > > > > > > Why would there be a different interface for controlling the flash in > > > simple cases and more complex cases? > > > > Sorry, not sure what you mean. Do you mean different APIs when the flash > > is controlled directly by the sensor and by an external controller? No, of > > course we need one API, but you either issue those ioctl()s to the sensor > > (sub)device, or to the dedicated flash (sub)device. If you mean my "minor > > subset" above, then I was trying to say, that this is a basis, that has to > > be extended, but not, that we will develop a new API for more complicated > > cases. > > I think I misunderstood you originally, sorry. I should have properly read the > RFC. :-) > > Your proposal of the flash mode is good, but what about software strobe (a > little more on that below)? > > Also, what about making this a V4L2 control instead?
These are two things, I think: first we have to decide which functions we need, second - how to implement them. Sure, controls are also a possibility. > The ADP1653 driver that > Laurent referred to implements flash control using V4L2 controls only. > > A version of the driver is here: > > <URL:http://gitorious.org/omap3camera/mainline/commit/a41027c857dfcbc268cf8d1c7c7d0ab8b6abac92> > > It's not yet in mainline --- one reason for this is the lack of time to > discuss a proper API for the flash. :-) > > ... > > > > > > This doesn't solve the flash/capture synchronization problem though. I > > > > > don't > > > > > think we need a dedicated snapshot capture mode at the V4L2 level. A > > > > > way to > > > > > configure the sensor to react on an external trigger provided by the > > > > > flash > > > > > controller is needed, and that could be a control on the flash > > > > > sub-device. > > > > > > > > Well... Sensors call this a "snapshot mode." I don't care that much how > > > > we > > > > _call_ it, but I do think, that we should be able to use it. > > > > > > Some sensors and webcams might have that, but newer camera solutions > > > tend to contain a raw bayer sensor and and ISP. There is no concept of > > > snapsnot mode in these sensors. > > > > Hm, I am not sure I understand, why sensors with DSPs in them should have > > no notion of a snapshot mode. Do they have no strobe / trigger pins? And > > no built in possibility to synchronize with a flash? > > I was referring to ISPs such as the OMAP 3 ISP. Some hardware have a flash > strobe pin while some doesn't (such as the N900). Of course, if no flash is present, you don't have to support it;) > Still, even if the strobe pin is missing it should be possible to allow > strobing the flash by using software strobe (usually an I2C message). > > I agree using a hardware strobe is much much better if it's available. Again - don't understand. Above (i2c message) you're referring to the sensor. But I don't think toggling the flash on per-frame basis from software via the sensor makes much sense. That way you could also just wire your flash to a GPIO. The main advantage of a sensor-controlled flash is, that is toggles the flash automatically, synchronised with its image read-out. You would, however, toggle the flash manually, if you just wanted to turn it on permanently (torch-mode). > > > > Hm, don't think only the "flash subdevice" has to know about this. > > > > First, > > > > you have to switch the sensor into that mode. Second, it might be either > > > > external trigger from the flash controller, or a programmed trigger and > > > > a > > > > flash strobe from the sensor to the flash (controller). Third, well, not > > > > quite sure, but doesn't the host have to know about the snapshot mode? > > > > > > I do not favour adding use case type of functionality to interfaces that > > > do not necessarily need it. Would the concept of a snapshot be > > > parametrisable on V4L2 level? > > > > I am open to this. I don't have a good idea of whether camera hosts have > > to know about the snapshot mode or not. It's open for discussion. > > What functionality would the snapshot mode provide? Flash synchronisation? > Something else? Also pre-defined number of images, enabling of the trigger pin and trigger i2c command. Just noticed - on mt9t031 and mt9v022 the snapshot mode also enables externally controlled exposure... > I have to admit I don't know of any hardware which would recognise a concept > of "snapshot". Do you have a smart sensor which does this, for example? The > only hardware support for the flash use I know of is the flash strobe signal. Several Aptina / Micron sensors have such a mode, e.g., mt9p031, mt9t031, mt9v022, mt9m001, also ov7725 from OmniVision (there it's called a "Single frame" mode), and, I presume, many others. And no, those are not some "smart" sensors, the ones from Aptina are pretty primitive Bayer / monochrome cameras. > Flash synchronisation is indeed an issue, and how to tell that a given frame > has been exposed with flash. The use of flash is just one of the parameters > which would be nice to connect to frames, though. Hm, yes, that's something to think about too... 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
