From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (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 5A4D2CA4E for ; Tue, 9 Jun 2026 06:29:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780986561; cv=none; b=tA5nBVniIhz3e5mZA9f2DUEKI6vEe1fY7PD6yCmnTuQCHIHrdnKqsJKIgIH2u9OCWdRU6NebmIgyJ9Iq1e3945wAZEE8RCpwl4rKsjm2S6aeGLN/LcXVZPuFkR3ZTqjXjkWILMNs2CPBF0beT8arUuLLSktDnQHEfg/jJmon3hE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780986561; c=relaxed/simple; bh=fFZb1LC7DcY797tSSsP0z+FIzp3MQTCV+pMWAcft1+E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QwuEuVMzpvM77KiOJPVrSQGfpWi3fb9ioroJA69VD5U024LQb6Ows5UfiIvCCrFKPJgsrlrSOC9vIAdr/3B16dSjZQzD4npEtbAelZ5ZiK940Hu9milA1Y3ZfGgfp0p17BcIKQ3JoFqCLX8SKOhNydihzCGQ8IZTY19Ewsb+bcs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=k4S+h/Jl; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="k4S+h/Jl" Received: from ideasonboard.com (93-46-82-201.ip106.fastwebnet.it [93.46.82.201]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id A3DA1132; Tue, 9 Jun 2026 08:28:49 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1780986529; bh=fFZb1LC7DcY797tSSsP0z+FIzp3MQTCV+pMWAcft1+E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k4S+h/JlUBY4RdAjkPHR+bNGBzpHxdgfVzONFOJitf7CqS5igtqdzH7hCNrE1+v1T ScfLmfGJjTX1SPJmmRcVsDhgh5SczUSn/opren8EkklfBnX1EQKtt96s0O0iiRJwAQ dNVAgxOQL+cFVI66qWIHSBjGghpc70IQLAyGOE0w= Date: Tue, 9 Jun 2026 08:29:14 +0200 From: Jacopo Mondi To: Laurent Pinchart Cc: Sakari Ailus , Jacopo Mondi , linux-media@vger.kernel.org, hans@jjverkuil.nl, Prabhakar , Kate Hsuan , Dave Stevenson , Tommaso Merciai , Benjamin Mugnier , Sylvain Petinot , Christophe JAILLET , Julien Massot , Naushir Patuck , "Yan, Dongcheng" , Stefan Klug , Mirela Rabulea , =?utf-8?B?QW5kcsOp?= Apitzsch , Heimir Thor Sverrisson , Kieran Bingham , Mehdi Djait , Ricardo Ribalda Delgado , Hans de Goede , Tomi Valkeinen , David Plowman , "Yu, Ong Hock" , "Ng, Khai Wen" , Jai Luthra , Rishikesh Donadkar Subject: Re: [PATCH v5 04/10] media: imx219: Make control handler ops for PIXEL_RATE NULL Message-ID: References: <20260607215356.842932-5-sakari.ailus@linux.intel.com> <20260608073653.GD370380@killaraus.ideasonboard.com> <20260608080338.GF370380@killaraus.ideasonboard.com> <20260608082426.GA380394@killaraus.ideasonboard.com> <20260608102755.GF772117@killaraus.ideasonboard.com> <20260608144200.GB380394@killaraus.ideasonboard.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260608144200.GB380394@killaraus.ideasonboard.com> Hi Laurent On Mon, Jun 08, 2026 at 05:42:00PM +0300, Laurent Pinchart wrote: > On Mon, Jun 08, 2026 at 04:47:03PM +0300, Sakari Ailus wrote: > > On Mon, Jun 08, 2026 at 01:27:55PM +0300, Laurent Pinchart wrote: > > > On Mon, Jun 08, 2026 at 01:21:22PM +0300, Sakari Ailus wrote: > > > > On Mon, Jun 08, 2026 at 11:24:26AM +0300, Laurent Pinchart wrote: > > > > > On Mon, Jun 08, 2026 at 11:14:32AM +0300, Sakari Ailus wrote: > > > > > > On Mon, Jun 08, 2026 at 11:03:38AM +0300, Laurent Pinchart wrote: > > > > > > > On Mon, Jun 08, 2026 at 09:53:17AM +0200, Jacopo Mondi wrote: > > > > > > > > Hi Laurent > > > > > > > > sorry if I reply in place of Sakari but I got this fresh > > > > > > > > > > > > > > Thanks :-) > > > > > > > > > > > > > > > On Mon, Jun 08, 2026 at 10:36:53AM +0300, Laurent Pinchart wrote: > > > > > > > > > On Mon, Jun 08, 2026 at 12:53:50AM +0300, Sakari Ailus wrote: > > > > > > > > > > The PIXEL_RATE control exists to convey the value to the userspace and has > > > > > > > > > > no configuration that would need to be programmed to the sensor. Make the > > > > > > > > > > control handler ops for the PIXEL_RATE control NULL and avoid a warning > > > > > > > > > > (as well as returning an error) from the driver. > > > > > > > > > > > > > > > > > > I thought the standard way to handle pixel rate being read only was to > > > > > > > > > set the V4L2_CTRL_FLAG_READ_ONLY flag, like we do for e.g. > > > > > > > > > V4L2_CID_LINK_FREQ. Is that not correct ? > > > > > > > > > > > > > > > > PIXEL_RATE is RO by default > > > > > > > > > > > > > > > > drivers/media/v4l2-core/v4l2-ctrls-defs.c: case V4L2_CID_PIXEL_RATE: > > > > > > > > drivers/media/v4l2-core/v4l2-ctrls-defs.c- *type = V4L2_CTRL_TYPE_INTEGER64; > > > > > > > > drivers/media/v4l2-core/v4l2-ctrls-defs.c- *flags |= V4L2_CTRL_FLAG_READ_ONLY; > > > > > > > > drivers/media/v4l2-core/v4l2-ctrls-defs.c- break; > > > > > > > > > > > > > > > > The purpose of setting the ctrl_ops member to NULL is to avoid having > > > > > > > > to handle RO controls in the driver implementation of .s_ctrl(). > > > > > > > > > > > > > > Shouldn't the V4L2 control framework avoid .s_ctrl() calls for read-only > > > > > > > controls ? I thought it did already. > > > > > > > > > > > > The control may be read-only on the UAPI but the driver could still do > > > > > > something about it in its s_ctrl() callback. I don't know if any driver > > > > > > depends on this though. > > > > > > > > > > It seems to be one of the many areas where control handling should be > > > > > simplified for drivers. > > > > > > > > > > In any case, the imx219 driver creates the V4L2_CID_LINK_FREQ control > > > > > with a non-NULL ops pointer, sets the V4L2_CTRL_FLAG_READ_ONLY flag, and > > > > > does not handle V4L2_CID_LINK_FREQ in imx219_set_ctrl(). If there's an > > > > > issue for V4L2_CID_PIXEL_RATE there is also an issue for > > > > > V4L2_CID_LINK_FREQ. > > > > > > > > The ops should be set to NULL for link_freq as well. > > > > > > > > > Maybe the best short term fix would be to drop the dev_info() in the > > > > > default case of the ctrl->id switch in imx219_set_ctrl() ? > > > > > > > > Any reason why not to set ops NULL instead? > > > > > > Because that seems to be a hack. Drivers shouldn't have to set a NULL > > > ops pointer for read-only controls, when there's already a read-only > > > flag. I'd like to simplify the code on the driver side and handle this > > > in the control framework, not adding yet another arcane rule that most > > > driver authors will not be aware of. > > > > I don't think I'd necessarily call it a hack. > > It's still yet another undocumented behaviour to will be copied through > cargo-cult in a subset of drivers, making the code base more difficult > to understand and maintain. The fact that this patch addressed the > PIXEL_RATE control but not the LINK_FREQUENCY control proves my concerns > are valid :-) > > I'd like to see one scheme clearly documented, and used by all drivers. > Let's first focus on selecting one scheme and documenting it. Hans' > opinion would be useful. > We discussed this very same matter a few months ago. Before having the framework handling this, by not calling into the driver's s_ctrl for RO controls, all users in-tree shall be checked to make sure they're actually not doing something with those RO controls. I even started a branch to check all drivers one-by-one and first set they're ops to NULL. I quickly got discouraged by the amount of work required and gave up. > > The control may be changeable, but not by the user. If the driver is just > > setting the value without going through the control framework, control > > events will be omitted. > > -- > Regards, > > Laurent Pinchart