Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933849AbbBQLSV (ORCPT ); Tue, 17 Feb 2015 06:18:21 -0500 Received: from aer-iport-2.cisco.com ([173.38.203.52]:27329 "EHLO aer-iport-2.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933831AbbBQLSU (ORCPT ); Tue, 17 Feb 2015 06:18:20 -0500 X-IronPort-AV: E=Sophos;i="5.09,594,1418083200"; d="scan'208";a="352261483" Message-ID: <54E32358.8010303@cisco.com> Date: Tue, 17 Feb 2015 12:17:44 +0100 From: Hans Verkuil User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.4.0 MIME-Version: 1.0 To: Ricardo Ribalda Delgado , Hans Verkuil , Mauro Carvalho Chehab , Sylwester Nawrocki , Antti Palosaari , Sakari Ailus , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] media/v4l2-ctrls: Always run s_ctrl on volatile ctrls References: <1424170934-18619-1-git-send-email-ricardo.ribalda@gmail.com> In-Reply-To: <1424170934-18619-1-git-send-email-ricardo.ribalda@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Authenticated-User: hansverk Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2238 Lines: 65 Hi Ricardo, On 02/17/15 12:02, Ricardo Ribalda Delgado wrote: > Volatile controls can change their value outside the v4l-ctrl framework. > > We should ignore the cached written value of the ctrl when evaluating if > we should run s_ctrl. > > Signed-off-by: Ricardo Ribalda Delgado > --- > > I have a control that tells the user when there has been a external trigger > overrun. (Trigger while processing old image). This is a volatile control. Does the application just read the control to check whether the trigger happened? Or is the control perhaps changed by an interrupt handler? > The user writes 0 to the control, to ack the error condition, and clear the > hardware flag. Would it be an idea to automatically ack the error condition when reading the control? Or, alternatively, have a separate button control to clear the condition. > > Unfortunately, it only works one time, because the next time the user writes > a zero to the control cluster_changed returns false. > > I think on volatile controls it is safer to run s_ctrl twice than missing a > valid s_ctrl. > > I know I am abusing a bit the API for this :P, but I also believe that the > semantic here is a bit confusing. The reason for that is that I have yet to see a convincing argument for allowing s_ctrl for a volatile control. Regards, Hans > > drivers/media/v4l2-core/v4l2-ctrls.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c > index 45c5b47..3d0c7f4 100644 > --- a/drivers/media/v4l2-core/v4l2-ctrls.c > +++ b/drivers/media/v4l2-core/v4l2-ctrls.c > @@ -1605,7 +1605,7 @@ static int cluster_changed(struct v4l2_ctrl *master) > > for (i = 0; i < master->ncontrols; i++) { > struct v4l2_ctrl *ctrl = master->cluster[i]; > - bool ctrl_changed = false; > + bool ctrl_changed = ctrl->flags & V4L2_CTRL_FLAG_VOLATILE; > > if (ctrl == NULL) > continue; > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/