> -----Original Message----- > From: Hans Verkuil [mailto:hverk...@xs4all.nl] > Sent: Wednesday, March 04, 2009 3:06 PM > To: sakari.ai...@maxwell.research.nokia.com > Cc: DongSoo(Nathaniel) Kim; Hiremath, Vaibhav; Toivonen Tuukka.O (Nokia- > D/Oulu); Aguirre Rodriguez, Sergio Alberto; linux-omap@vger.kernel.org; > Nagalla, Hari; linux-me...@vger.kernel.org > Subject: Re: [REVIEW PATCH 11/14] OMAP34XXCAM: Add driver > > On Wednesday 04 March 2009 20:22:04 Sakari Ailus wrote: > > Hans Verkuil wrote: > > > On Wednesday 04 March 2009 01:42:13 DongSoo(Nathaniel) Kim wrote: > > >> Thank you for your kind explanation Hans. > > >> > > >> Problem is omap3 camera subsystem is making device node for every int > > >> device attached to it. > > > > > > That's wrong. Multiple devices should only be created if they can all > > > be used at the same time. Otherwise there should be just one device > > > that uses S_INPUT et al to select between the inputs. > > > > There might be situations where multiple device nodes would be > > beneficial even if they cannot be used simultaneously in all cases. > > > > Currently the omap34xxcam camera driver creates one device per camera. A > > camera in this case contains an isp (or camera controller), image > > sensor, lens and flash. The properties like maximum frame rate or > > resolution of a camera are usually (almost) completely defined by those > > of the sensor, lens and flash. This affects also cropping capabilities. > > > > Several programs can access video devices simultaneously. What happens > > if another program switches the input when the first one doesn't expect > > it? The original user won't notice the change, instead of getting -EBUSY > > when trying to open the other video device. > > It is actually quite common to be able to switch inputs using one program > (e.g. v4l2-ctl) while another program also has the video node open. This > will typically be used for debugging or experimenting. Depending on the > hardware, switching inputs while capturing is in progress may or may not > be > allowed (the driver might just return -EBUSY in that case). > > In addition the application can also call VIDIOC_S_PRIORITY to protect it > against outside interference, provided the driver supports this ioctl. > > As an aside: many applications don't use VIDIOC_S_PRIORITY since whether a > driver implements it is hit-and-miss. As part of the new v4l2 framework I > have a struct v4l2_fh planned that will integrate support of this ioctl in > the framework, thus making it generic for all drivers. But this won't be > available any time soon.
As what I understand, we have 2 possible situations for multiple opens here: Situation 1 - Instance1: Select sensor 1, and Do queue/dequeue of buffers. - Instance2: If sensor 1 is currently selected, Begin loop requesting internally collected OMAP3ISP statistics (with V4L2 private based IOCTLs) for performing user-side Auto-exposure, Auto White Balance, Auto Focus algorithms. And Adjust gains (with S_CTRL) accordingly on sensor as a result. Situation 2 - Instance1: Select sensor1 as input. Begin streaming. - Instance2: Select sensor2 as input. Attempt to begin streaming. So, if I understood right, on Situation 2, if you attempt to do a S_INPUT to sensor2 while capturing from sensor1, it should return a -EBUSY, right? I mean, the app should consciously make sure the input (sensor) is the correct one before performing any adjustments. I think our current approach avoids the user to be constantly checking if the input is still the same before updating gains... I'm not clear if this single-node idea is really helping the user to have a simpler usage in Situation 1, which I feel will become pretty common on this driver... > > > In short, it's been just more clear to have one device per camera. There > > may be other reasons but these come to mind this time. > > I very much disagree here. Having multiple devices ONLY makes sense if you > can capture from them in parallel. This situation is really just a > straightforward case of multiple inputs you have to choose from. > > > > BTW, do I understand correctly that e.g. lens drivers also get their > > > own /dev/videoX node? Please tell me I'm mistaken! Since that would be > > > so very wrong. > > > > Yes, you're mistaken this time. :) > > > > The contents of a video devices are defined in platform data. > > > > > I hope that the conversion to v4l2_subdev will take place soon. You > are > > > basically stuck in a technological dead-end :-( > > > > Making things working properly in camera and ISP drivers has taken much > > more time than was anticipated and v4l2_subdev framework has developed a > > lot during that time. You're right --- we'll start thinking of how and > > when to move to v4l2_subdev. > > Just contact me if you have any questions, I'll be happy to help. If you > think there are missing bits in the framework, or find that you need to > workaround some limitation, please contact me first. It might well be that > I need to add something to support these devices, or that you should take > a > different approach instead. The sooner such issues are resolved, the less > time you loose. > > Regards, > > Hans > > -- > Hans Verkuil - video4linux developer - sponsored by TANDBERG -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
