From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout4.w1.samsung.com ([210.118.77.14]:15202 "EHLO mailout4.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422732AbbD2I6Z (ORCPT ); Wed, 29 Apr 2015 04:58:25 -0400 Received: from eucpsbgm1.samsung.com (unknown [203.254.199.244]) by mailout4.w1.samsung.com (Oracle Communications Messaging Server 7.0.5.31.0 64bit (built May 5 2014)) with ESMTP id <0NNK00IQW8XAY090@mailout4.w1.samsung.com> for linux-media@vger.kernel.org; Wed, 29 Apr 2015 09:58:22 +0100 (BST) Message-id: <55409D2C.8050007@samsung.com> Date: Wed, 29 Apr 2015 10:58:20 +0200 From: Jacek Anaszewski MIME-version: 1.0 To: Hans Verkuil Cc: linux-media , Ricardo Ribalda Delgado , Hans Verkuil , Sakari Ailus Subject: Re: S_CTRL must be called twice to set volatile controls References: <5540895A.5060102@samsung.com> <55408DE7.3020906@cisco.com> In-reply-to: <55408DE7.3020906@cisco.com> Content-type: text/plain; charset=windows-1252; format=flowed Content-transfer-encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi Hans, On 04/29/2015 09:53 AM, Hans Verkuil wrote: > Hi Jacek, > > On 04/29/15 09:33, Jacek Anaszewski wrote: >> Hi, >> >> After testing my v4l2-flash helpers patch [1] with the recent patches >> for v4l2-ctrl.c ([2] and [3]) s_ctrl op isn't called despite setting >> the value that should be aligned to the other step than default one. >> >> This happens for V4L2_CID_FLASH_TORCH_INTENSITY control with >> V4L2_CTRL_FLAG_VOLATILE flag. >> >> The situation improves after setting V4L2_CTRL_FLAG_EXECUTE_ON_WRITE >> flag for the control. Is this flag required now for volatile controls >> to be writable? > > Yes, you need that if you want to be able to write to a volatile control. > > It was added for exactly that purpose. Thanks for the explanation. > Why is V4L2_CID_FLASH_TORCH_INTENSITY volatile? Volatile typically only > makes sense if the hardware itself is modifying the value without the > software knowing about it. This can be the case for the flash LED devices that can reduce torch current when battery voltage level falls below predefined threshold. -- Best Regards, Jacek Anaszewski