Hi Richard, On Tue, Mar 18, 2025 at 03:46:18PM +0100, Richard Leitner wrote: > On Tue, Mar 18, 2025 at 02:06:50PM +0000, Sakari Ailus wrote: > > Hi Richard, > > > > On Tue, Mar 18, 2025 at 02:42:53PM +0100, Richard Leitner wrote: > > > On Tue, Mar 18, 2025 at 01:28:01PM +0000, Sakari Ailus wrote: > > > > Hi Richard, > > > > > > > > On Fri, Mar 14, 2025 at 05:08:16PM +0100, Richard Leitner wrote: > > > > > Hi Sakari, > > > > > > > > > > On Fri, Mar 14, 2025 at 01:34:07PM +0000, Sakari Ailus wrote: > > > > > > Hi Richard, > > > > > > > > > > > > On Fri, Mar 14, 2025 at 11:25:09AM +0100, Richard Leitner wrote: > > > > > > > On Fri, Mar 14, 2025 at 09:20:23AM +0000, Sakari Ailus wrote: > > > > > [...] > > > > > > > > On Fri, Mar 14, 2025 at 09:49:55AM +0100, Richard Leitner wrote: > > > > > > > > > Add a control V4L2_CID_FLASH_DURATION to set the duration of a > > > > > > > > > flash/strobe pulse. This is different to the V4L2_CID_FLASH_TIMEOUT > > > > > > > > > control, as the timeout defines a limit after which the flash is > > > > > > > > > "forcefully" turned off again. > > > > > > > > > > > > > > > > > > On the other hand the new V4L2_CID_FLASH_DURATION is the desired length > > > > > > > > > of the flash/strobe pulse > > > > > > > > > > > > > > > > What's the actual difference between the two? To me they appear the same, > > > > > > > > just expressed in a different way. > > > > > > > > > > > > > > According to FLASH_TIMEOUT documentation: > > > > > > > > > > > > > > Hardware timeout for flash. The flash strobe is stopped after this > > > > > > > period of time has passed from the start of the strobe. [1] > > > > > > > > > > > > > > This is a little bit unspecific, but as also discussed with Dave [2] > > > > > > > according to the documentation of V4L2_FLASH_FAULT_TIMEOUT it seems to > > > > > > > be targeted at providing a "real timeout" control, not settings the > > > > > > > desired duration: > > > > > > > > > > > > > > The flash strobe was still on when the timeout set by the user > > > > > > > --- V4L2_CID_FLASH_TIMEOUT control --- has expired. Not all flash > > > > > > > controllers may set this in all such conditions. [1] > > > > > > > > > > > > > > If I understood that wrong, I'm also happy to use FLASH_TIMEOUT for this > > > > > > > use-case. But tbh I think FLASH_DURATION would be more specific. > > > > > > > > > > > > > > As this still seems unclear: Should the documentation be > > > > > > > changed/rewritten if we stick with the FLASH_DURATION approach? > > > > > > > > > > > > > > [1] https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-flash.html > > > > > > > [2] https://lore.kernel.org/lkml/CAPY8ntB8i4OyUWAL8k899yUd5QsRifJXiOfWXKceGQ7TNZ4OUw@xxxxxxxxxxxxxx/ > > > > > > > > > > > > Right, I think I can see what you're after. > > > > > > > > > > > > How does the sensor determine when to start the strobe, i.e. on which frame > > > > > > and which part of the exposure of that frame? > > > > > > > > > > In general I think it's not part of V4L2_CID_FLASH_DURATION to take any > > > > > assumptions on that, as that's sensor/flash specific IMHO. > > > > > > > > > > In case of the ov9282 sensor driver (which is also part of this series) > > > > > the strobe is started synchronously with the exposure on each frame > > > > > start. > > > > > Being even more specific on the ov9292, the sensor also offers the > > > > > possibility to shift that strobe start in in either direction using a > > > > > register. Implementing this "flash shift" (as it's called in the sensors > > > > > datasheet) is currently under test on my side. I will likely send a > > > > > series for that in the coming weeks. > > > > > > > > Ok, so you get a single frame exposed with a flash when you start > > > > streaming, is that correct? > > > > > > Correct. The flash is switched on for the configured duration at every > > > frame exposure (the sensor has a global shutter) as long as the camera is > > > streaming. > > > > > > Maybe to following visualization of configured flash and exposure times help: > > > > > > _________ _________ _________ > > > exposure: __| |______| |______| |__ > > > > > > __ __ __ > > > flash: __| |_____________| |_____________| |_________ > > > ^^^^ > > > strobe_duration > > > > That diagram would work for global shutter but not for the much, much more > > common rolling shutter operation. Does the driver use the sensor in rolling > > shutter mode? This isn't very common with LED flashes. > > The ov9282 driver uses the sensor in global shutter mode. > > I totally agree with your statement. This pattern is only useful for > global shutter operation. I think (nearly?) all supported sensors use a rolling shutter. Could you include a comment on this to the driver? I wonder what Laurent thinks. -- Kind regards, Sakari Ailus
