From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 48DA520CCE7; Tue, 18 Mar 2025 15:11:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742310704; cv=none; b=Lvod8UeHiAv2qxS6LnSSgoL3PH2o/qkxjEHdF+1fLif+YNIkHIyHrst6PgNosZK8iEcdGgWSI0FEotwDTiURAHUcnPWUq3q0zbueRRnJ2B9thI6DU3hypbZH8yose5CfephbvtoFKo1yUcKUZP1cEuAOogG9Nq+LUGQ/2bWP8Mg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742310704; c=relaxed/simple; bh=CbQSibQRDXV8EGCExoS7jHIvFiOFpQOKGvG1oW99GKo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LWsVQGuMslBwDSYxkbAO/2ELtBRjHFQN92Tb2YW1YlsF24uEiB3cQ/lvTC3TymGLUDrcwN13DyyvrtfP3mt3vqoPqWypjwaO6GU8wDOv30P3REFWEoeVn6I5Hs+FX0mSIxi/sj2rYR4sqgEOf1i4Ct6H3qEC7jbI53lemj3eQZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=L8lgEmha; arc=none smtp.client-ip=198.175.65.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="L8lgEmha" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1742310702; x=1773846702; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=CbQSibQRDXV8EGCExoS7jHIvFiOFpQOKGvG1oW99GKo=; b=L8lgEmhaf7IpTV8UjIWrS2qvmbfY5nuuErWJwI7Ft6HLbt+AF5OlJa/0 glBvx7FCq58BM8hY+LZ8sjEQd8hK3onL8kJNGDDcfTgnd4RpezBRgO0Qn gMVocyCSQ5Ikzi+Q14IJqqKEos/fqWAF+G3OxdMwBketa5e5A+pODLVif 6eMwZ+M1zHqKYyxtRPfvK3cspQBj6PjJ9D3hxl3rElcdx6vxwHV6IJ2ZA iJW32MaMwkICo79Cdb3VIwpJ7uFjCZim/xl5gy4M8PHqf5+t9hJSzDpLV LZrcbI63VEgjBts9y6bnOuq0ksGfyy/YKX5vWotpm/BtQ1T7OOH/t3PIf w==; X-CSE-ConnectionGUID: lAcTZRuXTWqjyHvDeiqIog== X-CSE-MsgGUID: I1mmWIA0Q4yu6pzfrzrOWA== X-IronPort-AV: E=McAfee;i="6700,10204,11377"; a="54449467" X-IronPort-AV: E=Sophos;i="6.14,257,1736841600"; d="scan'208";a="54449467" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2025 08:11:41 -0700 X-CSE-ConnectionGUID: f53d1u82QMy8wfC3s1gVZw== X-CSE-MsgGUID: z1YzSif3R6WACjhwsw5Wmg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.14,257,1736841600"; d="scan'208";a="127394422" Received: from turnipsi.fi.intel.com (HELO kekkonen.fi.intel.com) ([10.237.72.44]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2025 08:11:40 -0700 Received: from kekkonen.localdomain (localhost [127.0.0.1]) by kekkonen.fi.intel.com (Postfix) with SMTP id A33A011F9BD; Tue, 18 Mar 2025 17:11:36 +0200 (EET) Date: Tue, 18 Mar 2025 15:11:36 +0000 Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo From: Sakari Ailus To: Richard Leitner Cc: Dave Stevenson , Mauro Carvalho Chehab , Lee Jones , Pavel Machek , Laurent Pinchart , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org Subject: Re: [PATCH v2 1/8] media: v4l: ctrls: add a control for flash/strobe duration Message-ID: References: <20250314-ov9282-flash-strobe-v2-0-14d7a281342d@linux.dev> <20250314-ov9282-flash-strobe-v2-1-14d7a281342d@linux.dev> <3dkwhfqxjhu3w4hpcl4gfsi22kwauo6s5urxrorezaw323yygq@nujmlkie5rpd> Precedence: bulk X-Mailing-List: linux-leds@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Richard, On Tue, Mar 18, 2025 at 03:46:18PM +0100, Richard Leitner wrote: > On Tue, Mar 18, 2025 at 02:06:50PM +0000, Sakari Ailus wrote: > > Hi Richard, > > > > On Tue, Mar 18, 2025 at 02:42:53PM +0100, Richard Leitner wrote: > > > On Tue, Mar 18, 2025 at 01:28:01PM +0000, Sakari Ailus wrote: > > > > Hi Richard, > > > > > > > > On Fri, Mar 14, 2025 at 05:08:16PM +0100, Richard Leitner wrote: > > > > > Hi Sakari, > > > > > > > > > > On Fri, Mar 14, 2025 at 01:34:07PM +0000, Sakari Ailus wrote: > > > > > > Hi Richard, > > > > > > > > > > > > On Fri, Mar 14, 2025 at 11:25:09AM +0100, Richard Leitner wrote: > > > > > > > On Fri, Mar 14, 2025 at 09:20:23AM +0000, Sakari Ailus wrote: > > > > > [...] > > > > > > > > On Fri, Mar 14, 2025 at 09:49:55AM +0100, Richard Leitner wrote: > > > > > > > > > Add a control V4L2_CID_FLASH_DURATION to set the duration of a > > > > > > > > > flash/strobe pulse. This is different to the V4L2_CID_FLASH_TIMEOUT > > > > > > > > > control, as the timeout defines a limit after which the flash is > > > > > > > > > "forcefully" turned off again. > > > > > > > > > > > > > > > > > > On the other hand the new V4L2_CID_FLASH_DURATION is the desired length > > > > > > > > > of the flash/strobe pulse > > > > > > > > > > > > > > > > What's the actual difference between the two? To me they appear the same, > > > > > > > > just expressed in a different way. > > > > > > > > > > > > > > According to FLASH_TIMEOUT documentation: > > > > > > > > > > > > > > Hardware timeout for flash. The flash strobe is stopped after this > > > > > > > period of time has passed from the start of the strobe. [1] > > > > > > > > > > > > > > This is a little bit unspecific, but as also discussed with Dave [2] > > > > > > > according to the documentation of V4L2_FLASH_FAULT_TIMEOUT it seems to > > > > > > > be targeted at providing a "real timeout" control, not settings the > > > > > > > desired duration: > > > > > > > > > > > > > > The flash strobe was still on when the timeout set by the user > > > > > > > --- V4L2_CID_FLASH_TIMEOUT control --- has expired. Not all flash > > > > > > > controllers may set this in all such conditions. [1] > > > > > > > > > > > > > > If I understood that wrong, I'm also happy to use FLASH_TIMEOUT for this > > > > > > > use-case. But tbh I think FLASH_DURATION would be more specific. > > > > > > > > > > > > > > As this still seems unclear: Should the documentation be > > > > > > > changed/rewritten if we stick with the FLASH_DURATION approach? > > > > > > > > > > > > > > [1] https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-flash.html > > > > > > > [2] https://lore.kernel.org/lkml/CAPY8ntB8i4OyUWAL8k899yUd5QsRifJXiOfWXKceGQ7TNZ4OUw@mail.gmail.com/ > > > > > > > > > > > > Right, I think I can see what you're after. > > > > > > > > > > > > How does the sensor determine when to start the strobe, i.e. on which frame > > > > > > and which part of the exposure of that frame? > > > > > > > > > > In general I think it's not part of V4L2_CID_FLASH_DURATION to take any > > > > > assumptions on that, as that's sensor/flash specific IMHO. > > > > > > > > > > In case of the ov9282 sensor driver (which is also part of this series) > > > > > the strobe is started synchronously with the exposure on each frame > > > > > start. > > > > > Being even more specific on the ov9292, the sensor also offers the > > > > > possibility to shift that strobe start in in either direction using a > > > > > register. Implementing this "flash shift" (as it's called in the sensors > > > > > datasheet) is currently under test on my side. I will likely send a > > > > > series for that in the coming weeks. > > > > > > > > Ok, so you get a single frame exposed with a flash when you start > > > > streaming, is that correct? > > > > > > Correct. The flash is switched on for the configured duration at every > > > frame exposure (the sensor has a global shutter) as long as the camera is > > > streaming. > > > > > > Maybe to following visualization of configured flash and exposure times help: > > > > > > _________ _________ _________ > > > exposure: __| |______| |______| |__ > > > > > > __ __ __ > > > flash: __| |_____________| |_____________| |_________ > > > ^^^^ > > > strobe_duration > > > > That diagram would work for global shutter but not for the much, much more > > common rolling shutter operation. Does the driver use the sensor in rolling > > shutter mode? This isn't very common with LED flashes. > > The ov9282 driver uses the sensor in global shutter mode. > > I totally agree with your statement. This pattern is only useful for > global shutter operation. I think (nearly?) all supported sensors use a rolling shutter. Could you include a comment on this to the driver? I wonder what Laurent thinks. -- Kind regards, Sakari Ailus