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 07C0129CA for ; Mon, 16 Dec 2024 13:51:58 +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=1734357120; cv=none; b=NPmuHwXVK34QGxt5D9K+lTlhGZoP5arB/0DTgrWbxIK1RmC29B6iOVmYRRvKJxm33AH9DfghvkjjqIVmDkxzlIPEtFaE1WgRACuZim8m4QNM9QxR7oZ/mzQgDnbrPH2HNX9fQLZ7bk2uayC92KCVhiuszccp/eMS4pw01BXlWpA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734357120; c=relaxed/simple; bh=eRk++64wIVp1j6QIVw3GPlcsFSHnW/6LsSn0cHj4/pM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dnVgqPfmyqfz7E09XLMFpNttKeVW6+TVPXadEVADEX3PMEQBVDDktiFXRPwRGi+rsJe5MvC6pr13JZM/SSTiSucR2Axv/Rifqzbh+aoYB4WlbDosRvk8/TQCjdi4x6bQWnwd262YisrZExLGePdsV1q/pFSbx21FVgN5SC+vtes= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (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=rDMGQpVk; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (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="rDMGQpVk" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 77C8082A; Mon, 16 Dec 2024 14:51:20 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1734357080; bh=eRk++64wIVp1j6QIVw3GPlcsFSHnW/6LsSn0cHj4/pM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rDMGQpVkV7lptmlfKRMpKdih+cW465uw2I+j/hydFvfbJOTeXW9ugWTaG3ZSciOaa 87bSZZHKw3z+zidbZ8ht3yuOAQnMI6GaSO8c9kCeh0eV5S8eWPBPRuvKDOUlbLF9q/ f0sN/YuTGUdQ+B7nj20rMTPIhnWWI+RgEzP2b8/k= Date: Mon, 16 Dec 2024 15:51:40 +0200 From: Laurent Pinchart To: Sakari Ailus Cc: linux-media@vger.kernel.org, Jacopo Mondi , hverkuil@xs4all.nl Subject: Re: [PATCH v7 2/5] media: v4l: Support obtaining link frequency via get_mbus_config Message-ID: <20241216135140.GA29336@pendragon.ideasonboard.com> References: <20241210075906.609490-1-sakari.ailus@linux.intel.com> <20241210075906.609490-3-sakari.ailus@linux.intel.com> <20241215165935.GG9975@pendragon.ideasonboard.com> <20241216111645.GL32204@pendragon.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, Dec 16, 2024 at 12:15:31PM +0000, Sakari Ailus wrote: > On Mon, Dec 16, 2024 at 01:16:45PM +0200, Laurent Pinchart wrote: > > On Mon, Dec 16, 2024 at 08:46:43AM +0000, Sakari Ailus wrote: > > > On Sun, Dec 15, 2024 at 06:59:35PM +0200, Laurent Pinchart wrote: > > > > On Tue, Dec 10, 2024 at 09:59:03AM +0200, Sakari Ailus wrote: > > > > > Add link_freq field to struct v4l2_mbus_config in order to pass the link > > > > > frequency to the receiving sub-device. > > > > > > > > The documentation of v4l2_get_link_freq() should be expanded to explain > > > > the new mode of operation. It should document which of the supported > > > > methods are recommended for new drivers. > > > > > > > > > > > > > > Signed-off-by: Sakari Ailus > > > > > --- > > > > > drivers/media/v4l2-core/v4l2-common.c | 11 ++++++++--- > > > > > include/media/v4l2-mediabus.h | 2 ++ > > > > > 2 files changed, 10 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c > > > > > index 9fe74c7e064f..88fbd5608f00 100644 > > > > > --- a/drivers/media/v4l2-core/v4l2-common.c > > > > > +++ b/drivers/media/v4l2-core/v4l2-common.c > > > > > @@ -508,13 +508,18 @@ EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_ctrl); > > > > > s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul, > > > > > unsigned int div) > > > > > { > > > > > + struct v4l2_mbus_config mbus_config = {}; > > > > > > > > Isn't mbus_config fully populated by the .get_mbus_config() operation ? > > > > That should be documented in the .get_mbus_config() operation > > > > documentation. > > > > > > It's a good practice to zero the memory before drivers get to work on it. I > > > presume drivers will set the fields that are relevant for them and ignore > > > the rest. > > > > > > I can add a note on get_mbus_config() the drivers should set all struct > > > fields to known values. > > > > Thanks. > > > > > > > struct v4l2_subdev *sd; > > > > > + int ret; > > > > > > > > > > sd = media_entity_to_v4l2_subdev(pad->entity); > > > > > - if (!sd) > > > > > - return -ENODEV; > > > > > + ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index, > > > > > + &mbus_config); > > > > > + if (ret < 0 && ret != -ENOIOCTLCMD) > > > > > + return ret; > > > > > > > > > > - return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div); > > > > > + return mbus_config.link_freq ?: > > > > > + __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div); > > > > > > > > if (mbus_config.link_freq) > > > > return mbus_config.link_freq; > > > > > > > > return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div); > > > > > > Whether this would be cleaner is debatable at least. I can switch if you > > > insist though. > > > > I think it's nicer. You could even write > > > > if (mbus_config.link_freq) > > return mbus_config.link_freq; > > > > /* > > * Fall back to using the link frequency control if the media bus config > > * doesn't provide a link frequency. > > */ > > return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div); > > I can use this. > > > > > > > I wonder if we should also add a message in case link_freq is 0, to get > > > > drivers to convert to reporting the link frequency through > > > > .get_mbus_config() if they already implement the operation. > > > > > > I'm not sure this will be useful: in most cases the LINK_FREQ control is > > > used and for a reason: it's user-configurable. Drivers should only populate > > > the field if the link frequency is determined by the driver. For the > > > receiver drivers it does not matter: they use v4l2_get_link_freq(). > > > > I think this depends on whether or not driver that have a configurable > > link frequency should report the current value through > > .get_mbus_config(). I think that drivers that implement > > .get_mbus_config() should, for consistency. > > We should have a helper that obtains information using get_mbus_config() as > well as the fwnode endpoint. I've proposed that a few times over the years. > I'm hoping for someone who needs dynamic configuration e.g. for lane > numbers to implement it. :-) I'm not sure to follow you here, I don't really see how it's related, or exactly what that helper would do. > I wouldn't try to add more burden for drivers on this. Beyond that, it's > common that if you have multiple implementations of something, one of them > (the unused one) eventually breaks. What we really need is to obtain the > information from the sub-device API, using the method the driver uses to > report it. We should have a single way to report a given piece of information, that would be the simplest for drivers and the least error prone. I think drivers should implement the LINK_FREQ control for userspace, and the .get_mbus_config() operation for kernel space. -- Regards, Laurent Pinchart