From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: exposure vs. exposure_absolute was Re: [PATCH v7 16/34] [media] add Omnivision OV5640 sensor driver Date: Thu, 1 Jun 2017 10:43:20 +0200 Message-ID: <20170601084320.GA16038@amd> 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> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5275355541614251345==" Return-path: In-Reply-To: <20170601082659.GJ1019@valkosipuli.retiisi.org.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: driverdev-devel-bounces@linuxdriverproject.org Sender: "devel" To: Sakari Ailus Cc: mark.rutland@arm.com, andrew-ct.chen@mediatek.com, minghsiu.tsai@mediatek.com, sakari.ailus@linux.intel.com, nick@shmanahar.org, songjun.wu@microchip.com, hverkuil@xs4all.nl, Steve Longerbeam , robert.jarzmik@free.fr, devel@driverdev.osuosl.org, markus.heiser@darmarIT.de, laurent.pinchart+renesas@ideasonboard.com, shuah@kernel.org, linux@armlinux.org.uk, geert@linux-m68k.org, Steve Longerbeam , linux-media@vger.kernel.org, devicetree@vger.kernel.org, kernel@pengutronix.de, arnd@arndb.de, mchehab@kernel.org, bparrot@ti.com, robh+dt@kernel.org, horms+renesas@verge.net.au, tiffany.lin@mediatek.com, linux-arm-kernel@lists.infradead.org, niklas.soderlund+renesas@ragnatech.se, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, jean-christophe.trotin@st.com, p.zabel@pengutronix.de, fabio.estevam@nxp.com, shawnguo@kerne List-Id: devicetree@vger.kernel.org --===============5275355541614251345== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="AqsLC8rIMeq19msA" Content-Disposition: inline --AqsLC8rIMeq19msA Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi! > > > + /* Auto/manual exposure */ > > > + ctrls->auto_exp =3D v4l2_ctrl_new_std_menu(hdl, ops, > > > + V4L2_CID_EXPOSURE_AUTO, > > > + V4L2_EXPOSURE_MANUAL, 0, > > > + V4L2_EXPOSURE_AUTO); > > > + ctrls->exposure =3D v4l2_ctrl_new_std(hdl, ops, > > > + V4L2_CID_EXPOSURE_ABSOLUTE, > > > + 0, 65535, 1, 0); > >=20 > > Is exposure_absolute supposed to be in microseconds...? >=20 > 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. >=20 > 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 --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --AqsLC8rIMeq19msA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlkv06gACgkQMOfwapXb+vICfgCeMAkZtS+dSZiIkxkVr86gjRq8 YxQAn3ECZOtpiTRU+5/M9tAD4g0C5lLu =qV/J -----END PGP SIGNATURE----- --AqsLC8rIMeq19msA-- --===============5275355541614251345== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ devel mailing list devel@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel --===============5275355541614251345==--