From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3B0CC433E6 for ; Mon, 15 Mar 2021 21:57:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D29864F07 for ; Mon, 15 Mar 2021 21:57:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231148AbhCOV4u (ORCPT ); Mon, 15 Mar 2021 17:56:50 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:41832 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231557AbhCOV4l (ORCPT ); Mon, 15 Mar 2021 17:56:41 -0400 Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BDA46316; Mon, 15 Mar 2021 22:56:39 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1615845400; bh=Mu/Bq32xgb1lbkO7ZIYXDgzir3coVjJSFFlMiEQD1Aw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k5OabQknRFg6nc2uM826ox3mrheQgLN9zxhL4Eburjz6/wl1fp7rwxDj/nIvdrvlj nFCWHxsyPSzK6q0YsMqJh16+jVUeNbmTzZr0u2SxMDwwQi4t62L63978VSAkvSCR7f DsR53pcvKBO6C/L2zz3K0wcG9AKT3iM30YepBtcc= Date: Mon, 15 Mar 2021 23:56:04 +0200 From: Laurent Pinchart To: Jacopo Mondi Cc: kieran.bingham+renesas@ideasonboard.com, niklas.soderlund+renesas@ragnatech.se, geert@linux-m68k.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, Hans Verkuil , Sakari Ailus Subject: Re: [PATCH v2 16/18] media: v4l2-subdev: De-deprecate init() subdev op Message-ID: References: <20210315131512.133720-1-jacopo+renesas@jmondi.org> <20210315131512.133720-17-jacopo+renesas@jmondi.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210315131512.133720-17-jacopo+renesas@jmondi.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jacopo, Thank you for the patch. On Mon, Mar 15, 2021 at 02:15:10PM +0100, Jacopo Mondi wrote: > The init() subdev core operation is deemed to be deprecated for new > subdevice drivers. However it could prove useful for complex > architectures to defer operation that require access to the > communication bus if said bus is not available (or fully configured) > at the time when the subdevice probe() function is run. > > As an example, the GMSL architecture requires the GMSL configuration > link to be configured on the host side after the remote subdevice > has completed its probe function. After the configuration on the host > side has been performed, the subdevice registers can be accessed through > the communication bus. > > In particular: > > HOST REMOTE > > probe() > | > ---------------------> | > probe() { > bus config() > } > |<--------------------| > v4l2 async bound { > bus config() > call subdev init() > |-------------------->| > init() { > access register on the bus() > } > |<------------------- > } > > In the GMSL use case the bus configuration requires the enablement of the > noise immunity threshold on the remote side which ensures reliability > of communications in electrically noisy environments. After the subdevice > has enabled the threshold at the end of its probe() sequence the host > side shall compensate it with an higher signal amplitude. Once this > sequence has completed the bus can be accessed with noise protection > enabled and all the operations that require a considerable number of > transactions on the bus (such as the image sensor configuration > sequence) are run in the subdevice init() operation implementation. I think this can be considered as a reasonable use of .init(). I'd like to get feedback from Hans and Sakari (CC'ed) though. > Signed-off-by: Jacopo Mondi > --- > include/media/v4l2-subdev.h | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h > index d0e9a5bdb08b..3068d9940669 100644 > --- a/include/media/v4l2-subdev.h > +++ b/include/media/v4l2-subdev.h > @@ -148,9 +148,18 @@ struct v4l2_subdev_io_pin_config { > * each pin being configured. This function could be called at times > * other than just subdevice initialization. > * > - * @init: initialize the sensor registers to some sort of reasonable default > - * values. Do not use for new drivers and should be removed in existing > - * drivers. > + * @init: initialize the subdevice registers to some sort of reasonable default > + * values. Do not use for new drivers (and should be removed in existing > + * ones) for regular architectures where the image sensor is connected to > + * the host receiver. For more complex architectures where the subdevice > + * initialization should be deferred to the completion of the probe > + * sequence of some intermediate component, or the communication bus > + * requires configurations on the host side that depend on the completion > + * of the probe sequence of the remote subdevices, the usage of this > + * operation could be considered to allow the devices along the pipeline to > + * probe and register in the media graph and to defer any operation that > + * require actual access to the communication bus to their init() function > + * implementation. > * > * @load_fw: load firmware. > * -- Regards, Laurent Pinchart