From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout1.w1.samsung.com ([210.118.77.11]:19705 "EHLO mailout1.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750934Ab3AGKql (ORCPT ); Mon, 7 Jan 2013 05:46:41 -0500 Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout1.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0MG9000SQ4KF9D30@mailout1.w1.samsung.com> for linux-media@vger.kernel.org; Mon, 07 Jan 2013 10:46:39 +0000 (GMT) Received: from [106.116.147.88] by eusync4.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTPA id <0MG900B074LR1B20@eusync4.samsung.com> for linux-media@vger.kernel.org; Mon, 07 Jan 2013 10:46:39 +0000 (GMT) Message-id: <50EAA78E.4090904@samsung.com> Date: Mon, 07 Jan 2013 11:46:38 +0100 From: Andrzej Hajda MIME-version: 1.0 To: linux-media@vger.kernel.org Cc: Sylwester Nawrocki Subject: RFC: add parameters to V4L controls Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi, I have included this proposition already in the post "[PATCH RFC 0/2] V4L: Add auto focus area control and selection" but it left unanswered. I repost it again in a separate e-mail, I hope this way it will be easier to attract attention. Problem description Currently V4L2 controls can have only single value (of type int, int64, string). Some hardware controls require more than single int parameter, for example to set auto-focus (AF) rectangle four coordinates should be passed, to set auto-focus spot two coordinates should be passed. Current solution In case of AF rectangle we can reuse selection API as in "[PATCH RFC 0/2] V4L: Add auto focus area control and selection" post. Pros: - reuse existing API, Cons: - two IOCTL's to perform one action, - non-atomic operation, - fits well only for rectangles and spots (but with unused fields width, height), in case of other parameters we should find a different way. Proposed solution The solution takes an advantage of the fact VIDIOC_(G/S/TRY)_EXT_CTRLS ioctls can be called with multiple controls per call. I will present it using AF area control example. There could be added four pseudo-controls, lets call them for short: LEFT, TOP, WIDTH, HEIGHT. Those controls could be passed together with V4L2_AUTO_FOCUS_AREA_RECTANGLE control in one ioctl as a kind of parameters. For example setting auto-focus spot would require calling VIDIOC_S_EXT_CTRLS with the following controls: - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE - LEFT = ... - RIGHT = ... Setting AF rectangle: - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE - LEFT = ... - TOP = ... - WIDTH = ... - HEIGHT = ... Setting AF object detection (no parameters required): - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION I have presented all three cases to show the advantages of this solution: - atomicity - control and its parameters are passed in one call, - flexibility - we are not limited by a fixed number of parameters, - no-redundancy - we can pass only required parameters (no need to pass null width and height in case of spot selection), - extensibility - it is possible to extend parameters in the future, for example add parameters to V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION, without breaking API, - backward compatibility, - re-usability - this schema could be used in other controls, pseudo-controls could be re-used in other controls as well. - API backward compatibility. Regards Andrzej Hajda