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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 0902BC433FE for ; Thu, 23 Sep 2021 10:03:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE0E061279 for ; Thu, 23 Sep 2021 10:03:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240356AbhIWKFK (ORCPT ); Thu, 23 Sep 2021 06:05:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240296AbhIWKFI (ORCPT ); Thu, 23 Sep 2021 06:05:08 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D94AC061574; Thu, 23 Sep 2021 03:03:37 -0700 (PDT) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id D9A7E45E; Thu, 23 Sep 2021 12:03:35 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1632391416; bh=QWEG82V5G7D0G117wXh9PFLZKVi96y001Ge/iBI4Nxk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YREPVEVszHxTtgJ8ePsrRFxMpTg956Y4W/xYvS5yhCMQYBzgqN8sRz2pfXKX8sX3f Q8BfEuhf+lrgglRu+aPqfsJ98pNEX4cnEfJb0cm64sQL6jGoUMJVBcb0GcR7DHQLjN jZdpD6MsRIuMO/lo2TyDgs0J/otY4hiL09L9KXIQ= Date: Thu, 23 Sep 2021 13:03:34 +0300 From: Laurent Pinchart To: "H. Nikolaus Schaller" Cc: Paul Cercueil , David Airlie , Daniel Vetter , linux-mips , list@opendingux.net, dri-devel , linux-kernel , Paul Boddie Subject: Re: [PATCH v3 6/6] drm/ingenic: Attach bridge chain to encoders Message-ID: References: <20210922205555.496871-1-paul@crapouillou.net> <20210922205555.496871-7-paul@crapouillou.net> <32234186-1802-4FDF-801A-B14E48FB86D8@goldelico.com> <896D04E4-4058-474B-8BD2-7F21B1C754E4@goldelico.com> <3764505C-7CA9-40C4-8CFA-8B0F2361E6D5@goldelico.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <3764505C-7CA9-40C4-8CFA-8B0F2361E6D5@goldelico.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Nikolaus, On Thu, Sep 23, 2021 at 11:55:56AM +0200, H. Nikolaus Schaller wrote: > > Am 23.09.2021 um 11:27 schrieb Laurent Pinchart: > > On Thu, Sep 23, 2021 at 11:19:23AM +0200, H. Nikolaus Schaller wrote: > >> > >>>>> + ret = drm_bridge_attach(encoder, &ib->bridge, NULL, > >>>>> + DRM_BRIDGE_ATTACH_NO_CONNECTOR); > >>>> > >>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR makes it fundamentally incompatible > >>>> with synopsys/dw_hdmi.c > >>>> That driver checks for DRM_BRIDGE_ATTACH_NO_CONNECTOR being NOT present, > >>>> since it wants to register its own connector through dw_hdmi_connector_create(). > >>>> It does it for a reason: the dw-hdmi is a multi-function driver which does > >>>> HDMI and DDC/EDID stuff in a single driver (because I/O registers and power > >>>> management seem to be shared). > >>> > >>> The IT66121 driver does all of that too, and does not need > >>> DRM_BRIDGE_ATTACH_NO_CONNECTOR. The drm_bridge_funcs struct has > >>> callbacks to handle cable detection and DDC stuff. > >>> > >>>> Since I do not see who could split this into a separate bridge and a connector driver > >>>> and test it on multiple SoC platforms (there are at least 3 or 4), I think modifying > >>>> the fundamentals of the dw-hdmi architecture just to get CI20 HDMI working is not > >>>> our turf. > >>> > >>> You could have a field in the dw-hdmi pdata structure, that would > >>> instruct the driver whether or not it should use the new API. Ugly, > >>> I know, and would probably duplicate a lot of code, but that would > >>> allow other drivers to be updated at a later date. > >> > >> Yes, would be very ugly. > >> > >> But generally who has the knowledge (and time) to do this work? > >> And has a working platform to test (jz4780 isn't a good development environment)? > >> > >> The driver seems to have a turbulent history starting 2013 in staging/imx and > >> apparently it was generalized since then... Is Laurent currently dw-hdmi maintainer? > > > > "Maintainer" would be an overstatement. I've worked on that driver in > > the past, and I still use it, but don't have time to really maintain it. > > I've also been told that Synopsys required all patches for that driver > > developed using documentation under NDA to be submitted internally to > > them first before being published, so I decided to stop contributing > > instead of agreeing with this insane process. There's public > > documentation about the IP in some NXP reference manuals though, so it > > should be possible to still move forward without abiding by this rule. > > > >>>> Therefore the code here should be able to detect if drm_bridge_attach() already > >>>> creates and attaches a connector and then skip the code below. > >>> > >>> Not that easy, unfortunately. On one side we have dw-hdmi which > >>> checks that DRM_BRIDGE_ATTACH_NO_CONNECTOR is not set, and on the > >>> other side we have other drivers like the IT66121 which will fail if > >>> this flag is not set. > >> > >> Ok, I see. You have to handle contradicting cases here. > >> > >> Would it be possible to run it with DRM_BRIDGE_ATTACH_NO_CONNECTOR first > >> and retry if it fails without? > >> > >> But IMHO the return value (in error case) is not well defined. So there > >> must be a test if a connector has been created (I do not know how this > >> would work). > >> > >> Another suggestion: can you check if there is a downstream connector defined in > >> device tree (dw-hdmi does not need such a definition)? > >> If not we call it with 0 and if there is one we call it with > >> DRM_BRIDGE_ATTACH_NO_CONNECTOR and create one? > > > > I haven't followed the ful conversation, what the reason why > > DRM_BRIDGE_ATTACH_NO_CONNECTOR can't always be use here ? > > The synopsys driver creates its own connector through dw_hdmi_connector_create() > because the IP handles DDC/EDID directly. That doesn't require creating a connector though. The driver implements drm_bridge_funcs.get_edid(), which is used to get the EDID without the need to create a connector in the dw-hdmi driver. > Hence it checks for ! DRM_BRIDGE_ATTACH_NO_CONNECTOR which seems to be the > right thing to do on current platforms that use it. > > For CI20/jz4780 we just add a specialisation of the generic dw-hdmi to > make HDMI work. > > Now this patch for drm/ingenic wants the opposite definition and create its own > connector. This fails even if we remove the check (then we have two interfering > connectors). > > > We're moving > > towards requiring DRM_BRIDGE_ATTACH_NO_CONNECTOR for all new code, so it > > will have to be done eventually. > > So from my view drm/ingenic wants to already enforce this rule and breaks dw-hdmi. > > IMHO it should either handle this situation gracefully or include a fix for > dw-hdmi.c to keep it compatible. -- Regards, Laurent Pinchart