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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 23151C04EBD for ; Tue, 16 Oct 2018 13:11:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CA13B20866 for ; Tue, 16 Oct 2018 13:11:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="DV8lF0x+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CA13B20866 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727067AbeJPVCW (ORCPT ); Tue, 16 Oct 2018 17:02:22 -0400 Received: from perceval.ideasonboard.com ([213.167.242.64]:39504 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726760AbeJPVCW (ORCPT ); Tue, 16 Oct 2018 17:02:22 -0400 Received: from avalon.localnet (dfj612ybrt5fhg77mgycy-3.rev.dnainternet.fi [IPv6:2001:14ba:21f5:5b00:2e86:4862:ef6a:2804]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id DFDD61A81; Tue, 16 Oct 2018 15:11:53 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1539695514; bh=WhpwMLDcD+2DL28YK/oI4T0/BRuG4A3tzuGsy4ldtX0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DV8lF0x+lMfDyxfzS6KCigWxbT8kp/Lq/R/Byy7w+QmrSOmqg6nmPkijNVTVsniyo U3YS7/7O05EhAPXc4gQH5Cw0Y0E1htjTWKOYQQJ1WS8BYgPVwYEp6lO6dplgr0ppUc XD9qcusjv/sX9St9vCIoicMmosH3Hb6/a7oYt9dQ= From: Laurent Pinchart To: Vladimir Zapolskiy Cc: kieran.bingham@ideasonboard.com, Lee Jones , Vladimir Zapolskiy , Linus Walleij , Rob Herring , Marek Vasut , Wolfram Sang , devicetree@vger.kernel.org, linux-gpio@vger.kernel.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/7] mfd: ds90ux9xx: add TI DS90Ux9xx de-/serializer MFD driver Date: Tue, 16 Oct 2018 16:12:02 +0300 Message-ID: <6392366.NPbusjoGUK@avalon> Organization: Ideas on Board Oy In-Reply-To: <369ef3ac-6f68-c450-713f-762b1c5cd5c9@mentor.com> References: <20181008211205.2900-1-vz@mleia.com> <3599186.afdMBtdL0k@avalon> <369ef3ac-6f68-c450-713f-762b1c5cd5c9@mentor.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vladimir, On Saturday, 13 October 2018 18:10:25 EEST Vladimir Zapolskiy wrote: > On 10/12/2018 04:01 PM, Laurent Pinchart wrote: > > On Friday, 12 October 2018 14:47:52 EEST Kieran Bingham wrote: > >> On 12/10/18 11:58, Vladimir Zapolskiy wrote: > [snip] > > >> Essentially they are multi purpose buses - which do not yet have a home. > >> We have used media as a home because of our use case. > >> > >> The use case whether they transfer frames from a camera or to a display > >> are of course closely related, but ultimately covered by two separate > >> subsystems at the pixel level (DRM vs V4L, or other for other data) > >> > >> Perhaps as they are buses - on a level with USB or I2C (except they can > >> of course carry I2C or Serial as well as 'bi-directional video' etc ), > >> they are looking for their own subsystem. > >> > >> Except I don't think we don't want to add a new subsystem for just one > >> (or two) devices... > > > > I'm not sure a new subsystem is needed. As you've noted there's an overlap > > between drivers/media/ and drivers/gpu/drm/ in terms of supported > > hardware. We even have a devices supported by two drivers, one in drivers/ > > media/ and one in drivers/gpu/drm/ (I'm thinking about the adv7511 in > > particular). This is a well known issue, and so far nothing has been done > > in mainline to try and solve it. > > I agree that there's an overlap between drivers/media/ and drivers/gpu/drm/, > formally a hypothetical (sic!) DS90Ux9xx video bridge cell driver should be > added into both subsystems also, and the actual driver of two should be > selected in runtime. I call such a driver 'hypothetical', because in fact I > don't have it, and I'm not so sure that its existence is justified, but > that's only because DS90Ux9xx video bridge functionality is _transparent_, > it does not have any controls literally, but it is a pure luck eventually. I don't think that's entirely correct, there's at least the video bus width (18-bit/24-bit) that needs to be selected. You currently do so through a pinctrl property, but that's not right. > So, as I've stated in my cover letter, I can misuse yours 'lvds-encoder' > driver only for the purpose of establishing a mediated link between > an LVDS controller and a panel over a serializer-deserializer pair. > > > Trying to find another home in drivers/mfd/ to escape from the problem > > isn't a good solution in my opinion. The best option from a Linux point > > of view would be to unify V4L2 and DRM/KMS when it comes to bridge > > support, but that's a long way down the road (I won't complain if you > > want to give it a go though> > > :-)). > > I return you a wider smile :) > > > As your use cases are display, focused, I would propose to start with > > drivers/gpu/drm/bridge/, and leave the problem of camera support for first > > person who will have such a use case. > > Frankly speaking I would like to start from copy-pasting your 'lvds-encoder' > driver into an 'absolutely-transparent-video-bridge' driver with no LVDS or > 'encoder' specifics, adding just a new compatible may suffice, if the > driver is renamed/redefined. > > PS, I remember I owe you a reference OF snippet of data path to a panel. -- Regards, Laurent Pinchart