From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp1-g21.free.fr ([212.27.42.1]:35444 "EHLO smtp1-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756567Ab2D0HwQ convert rfc822-to-8bit (ORCPT ); Fri, 27 Apr 2012 03:52:16 -0400 Date: Fri, 27 Apr 2012 09:53:09 +0200 From: Jean-Francois Moine To: Antonio Ospite Cc: linux-media@vger.kernel.org, Erik =?UTF-8?B?QW5kcsOpbg==?= Subject: Re: gspca V4L2_CID_EXPOSURE_AUTO and VIDIOC_G/S/TRY_EXT_CTRLS Message-ID: <20120427095309.5d922000@tele> In-Reply-To: <20120418153720.1359c7d2f2a3efc2c7c17b88@studenti.unina.it> References: <20120418153720.1359c7d2f2a3efc2c7c17b88@studenti.unina.it> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-media-owner@vger.kernel.org List-ID: On Wed, 18 Apr 2012 15:37:20 +0200 Antonio Ospite wrote: > I noticed that AEC (Automatic Exposure Control, or > V4L2_CID_EXPOSURE_AUTO) does not work in the ov534 gspca driver, either > from guvcview or qv4l2. [snip] > So in ov534, but I think in m5602 too, V4L2_CID_EXPOSURE_AUTO does not > work from guvcview, qv4l2, or v4l2-ctrl, for instance the latter fails > with the message: > > error 25 getting ext_ctrl Auto Exposure > > I tried adding an hackish implementation of vidioc_g_ext_ctrls and > vidioc_s_ext_ctrls to gspca, and with these V4L2_CID_EXPOSURE_AUTO seems > to work, but I need to learn more about this kind of controls before > I can propose a decent implementation for mainline inclusion myself, so > if anyone wants to anticipate me I'd be glad to test :) > > Unrelated, but maybe worth mentioning is that V4L2_CID_EXPOSURE_AUTO is > of type MENU, while some drivers are treating it as a boolean, I think > I can fix this one if needed. Hi Antonio, Yes, V4L2_CID_EXPOSURE_AUTO is of class V4L2_CTRL_CLASS_CAMERA, and, as the associated menu shows, it is not suitable for webcams. In the webcam world, the autoexposure is often the same as the autogain: in the knee algorithm (http://81.209.78.62:8080/docs/LowLightOptimization.html - also look at gspca/sonixb.c), both exposure and gain are concerned. The cases where a user wants only autoexposure (fixed gain) or autogain (fixed exposure) are rare. If you want people to be able to do that, you should add a new webcam control, V4L2_CID_AUTOEXPOSURE, and also add it to each driver which implements the knee algorithm, and handle the three cases, autogain only, autoexposure only and knee. Then, looking about your implementation of vidioc_s_ext_ctrls, I found it was a bit simple: setting many controls is atomic, i.e., if any error occurs at some point, the previous controls should be reset to their original values. Same about vidioc_g_ext_ctrls: the mutex must be taken only once for the values do not change. You also do not check if the controls are in a same control class. Anyway, are these ioctl's needed? Regards. -- Ken ar c'hentañ | ** Breizh ha Linux atav! ** Jef | http://moinejf.free.fr/