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 A6E753EC2F7 for ; Mon, 8 Jun 2026 14:42:05 +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=1780929727; cv=none; b=r9qkK8THrqzNxsJd5oTtKgZ1AUh8GOGdxpVHTHBu5TJ3MgzutbeF5fXa+IWmTnl7S6Bub7NTIt97s7wjzySE6kHFTysDtWk8BiqQiEiK1CJ+zNnL/EV1MJwyg2rdoWHVb1HomyRb7d5H1CPmDR4oIAAIXIsqmTstvrLPwWkh5Ek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780929727; c=relaxed/simple; bh=YHxid97Kffr9RKo3SboMCIdkuqcCSOevLEackEJCrGI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HQcg5Dkr1yXOZ1jZ9MnCuJWiIieBl/zxkdkpsCkmi9+hhpWf9Sx0BGZg2DJ9EWUz92SEaiZJLb4c/bclwcaimEZFSVwZHcIl6O48NIpA+4XOHOs99i010zcZjDaajPiq9pUdGKFunq+e4edrw4bfvapVuN7iTEVkw+Py/jS0K/k= 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=pQe3JKux; 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="pQe3JKux" Received: from killaraus.ideasonboard.com (2001-14ba-70f3-e800--a06.rev.dnainternet.fi [IPv6:2001:14ba:70f3:e800::a06]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id F2B5FD0; Mon, 8 Jun 2026 16:41:33 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1780929694; bh=YHxid97Kffr9RKo3SboMCIdkuqcCSOevLEackEJCrGI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pQe3JKux/0dF+p3mIhy563ygiS9EThWkNZMCus1ckbgA4RkNqhddxXFIyOTVaO65l faS6BWd5KWA4kpij1HCH6iFfPrLfgIUPzfObGKnWnWoTazjleBFXzZGNSHpvVENhLW jy4ngg9+oEdhz1T4Zh1sx5Moxyw7Ni6U6yjyN4TI= Date: Mon, 8 Jun 2026 17:42:00 +0300 From: Laurent Pinchart To: Sakari Ailus Cc: 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: <20260608144200.GB380394@killaraus.ideasonboard.com> References: <20260607215356.842932-1-sakari.ailus@linux.intel.com> <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> 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: 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. > 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