From mboxrd@z Thu Jan 1 00:00:00 1970 From: pavel@ucw.cz (Pavel Machek) Date: Thu, 1 Jun 2017 10:43:20 +0200 Subject: exposure vs. exposure_absolute was Re: [PATCH v7 16/34] [media] add Omnivision OV5640 sensor driver In-Reply-To: <20170601082659.GJ1019@valkosipuli.retiisi.org.uk> References: <1495672189-29164-1-git-send-email-steve_longerbeam@mentor.com> <1495672189-29164-17-git-send-email-steve_longerbeam@mentor.com> <20170531195821.GA16962@amd> <20170601082659.GJ1019@valkosipuli.retiisi.org.uk> Message-ID: <20170601084320.GA16038@amd> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi! > > > + /* Auto/manual exposure */ > > > + ctrls->auto_exp = v4l2_ctrl_new_std_menu(hdl, ops, > > > + V4L2_CID_EXPOSURE_AUTO, > > > + V4L2_EXPOSURE_MANUAL, 0, > > > + V4L2_EXPOSURE_AUTO); > > > + ctrls->exposure = v4l2_ctrl_new_std(hdl, ops, > > > + V4L2_CID_EXPOSURE_ABSOLUTE, > > > + 0, 65535, 1, 0); > > > > Is exposure_absolute supposed to be in microseconds...? > > Yes. OTOH V4L2_CID_EXPOSURE has no defined unit, so it's a better fit IMO. > Way more drivers appear to be using EXPOSURE than EXPOSURE_ABSOLUTE, too. > > Ideally we should have only one control for exposure. No. N-o. No no no. NO! No. N-o. NONONO. No. NooooooooooOOO!!!!!!!!!!!!! Sorry, no. Userspace needs to know exposure times. It is not so important for a webcam, but it is mandatory for digital camera. As it gets darker, autogain wants to scale exposure to cca 1/100 sec, then it wants to scale gain up to maximum, and only then it wants to continue scaling exposure. (Threshold will be shorter in "sports" mode, perhaps 1/300sec?) Plus, we want user to be able to manually set exposure parameters. So... _this_ driver probably should use V4L2_CID_EXPOSURE. (If the units are not known). But in general we'd prefer drivers using V4L2_CID_EXPOSURE_ABSOLUTE. Your car has speedometer calibrated in km/h or mph, not in "% of max", right? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 181 bytes Desc: Digital signature URL: