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 5EAA3C12002 for ; Wed, 21 Jul 2021 12:05:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B1966120C for ; Wed, 21 Jul 2021 12:05:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234249AbhGULZU (ORCPT ); Wed, 21 Jul 2021 07:25:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51058 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236463AbhGULY7 (ORCPT ); Wed, 21 Jul 2021 07:24:59 -0400 Received: from mail-wr1-x434.google.com (mail-wr1-x434.google.com [IPv6:2a00:1450:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F2AFBC0613E0 for ; Wed, 21 Jul 2021 05:05:04 -0700 (PDT) Received: by mail-wr1-x434.google.com with SMTP id f17so1916922wrt.6 for ; Wed, 21 Jul 2021 05:05:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=z6z6wcsCD0sgswylDcSLb5hJNlUUlxqeQM6i1pyENB8=; b=Pwmq/YdDmpsIlO2A2QRk6mJt4pqqfcVj1+GAnKLpdRZROoy1WP0Ahtu6IsX2NZCwey I6B62etiKj6ilJ+LvoSviQJkvnmZVR/NG75sDFjoi4ZnZliV1t89Ql2qqttaXT13dkFF LAQ4NrxOZIkMLM5mItPLq7SIiJUUHGlAwHLSc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=z6z6wcsCD0sgswylDcSLb5hJNlUUlxqeQM6i1pyENB8=; b=QyoKlTIyBXtUhDTPq6C0L84dz+7496RgKS/tiLw6JlseM54MFBnbJ9YdDutNxI3Yo+ dHKWqbYGLja2NvaLKtt2OiMqe9vKGpsQsLy9Y1f4nXfe7CHBiHJxBX8jSXVI5Iu73riU zgV5YBQfwenPOR9+R4sebRiWVvKMnQgQABH20LdvZLrPGH7RLohhc9VeP7d/b6nK2PTM vL6Ui2f6tRRzis/08dZJLKUDxfJtNYWqGPqPPUTyZKGZ8vPG3KTebEGLfVhf9bQQvRml 6XQOJ2EKsKEualDQdOLY2dQao9CYkRvee1qk62AI793wRQ/oSD0D/zZF9BUsbu2P4xJq 7/Ww== X-Gm-Message-State: AOAM531uOzb1sEiGsWWVgYJNpbb5FMMKt3V2vr/2QmBiDt21Yy+6oDLa dQFsvQOUCQQ+5SJ9a7vXKvHtAw== X-Google-Smtp-Source: ABdhPJysxSwXxGVP2K2pQwV/yw6g/ztlYnUO5QhknYExb/6qci30zTKDiDX0fOLM3erwYlbkfytHoA== X-Received: by 2002:a5d:5550:: with SMTP id g16mr10124556wrw.342.1626869103477; Wed, 21 Jul 2021 05:05:03 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id z7sm13593957wrt.94.2021.07.21.05.05.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Jul 2021 05:05:03 -0700 (PDT) Date: Wed, 21 Jul 2021 14:05:01 +0200 From: Daniel Vetter To: Maxime Ripard Cc: Robert Foss , Andrzej Hajda , Daniel Vetter , David Airlie , Sam Ravnborg , Maarten Lankhorst , Thomas Zimmermann , Neil Armstrong , Jonas Karlman , Jernej Skrabec , Thierry Reding , Laurent Pinchart , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges Message-ID: Mail-Followup-To: Maxime Ripard , Robert Foss , Andrzej Hajda , Daniel Vetter , David Airlie , Sam Ravnborg , Maarten Lankhorst , Thomas Zimmermann , Neil Armstrong , Jonas Karlman , Jernej Skrabec , Thierry Reding , Laurent Pinchart , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20210720134525.563936-1-maxime@cerno.tech> <20210720134525.563936-5-maxime@cerno.tech> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210720134525.563936-5-maxime@cerno.tech> X-Operating-System: Linux phenom 5.10.0-7-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 20, 2021 at 03:45:19PM +0200, Maxime Ripard wrote: > Interactions between bridges, panels, MIPI-DSI host and the component > framework are not trivial and can lead to probing issues when > implementing a display driver. Let's document the various cases we need > too consider, and the solution to support all the cases. > > Signed-off-by: Maxime Ripard I still have this dream that eventually we resurrect a patch to add device_link to bridges/panels (ideally automatically), to help with some of the suspend/resume issues around here. Will this make things worse? I think it'd be really good to figure that out with some coding, since if we have incompatible solution to handle probe issues vs suspend/resume issues, we're screwed. Atm the duct-tape is to carefully move things around between suspend and suspend_early hooks (and resume and resume_late) and hope it all works ... -Daniel > --- > Documentation/gpu/drm-kms-helpers.rst | 6 +++ > drivers/gpu/drm/drm_bridge.c | 60 +++++++++++++++++++++++++++ > 2 files changed, 66 insertions(+) > > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst > index 10f8df7aecc0..ec2f65b31930 100644 > --- a/Documentation/gpu/drm-kms-helpers.rst > +++ b/Documentation/gpu/drm-kms-helpers.rst > @@ -157,6 +157,12 @@ Display Driver Integration > .. kernel-doc:: drivers/gpu/drm/drm_bridge.c > :doc: display driver integration > > +Special Care with MIPI-DSI bridges > +---------------------------------- > + > +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c > + :doc: special care dsi > + > Bridge Operations > ----------------- > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > index c9a950bfdfe5..81f8dac12367 100644 > --- a/drivers/gpu/drm/drm_bridge.c > +++ b/drivers/gpu/drm/drm_bridge.c > @@ -95,6 +95,66 @@ > * documentation of bridge operations for more details). > */ > > +/** > + * DOC: special care dsi > + * > + * The interaction between the bridges and other frameworks involved in > + * the probing of the display driver and the bridge driver can be > + * challenging. Indeed, there's multiple cases that needs to be > + * considered: > + * > + * - The display driver doesn't use the component framework and isn't a > + * MIPI-DSI host. In this case, the bridge driver will probe at some > + * point and the display driver should try to probe again by returning > + * EPROBE_DEFER as long as the bridge driver hasn't probed. > + * > + * - The display driver doesn't use the component framework, but is a > + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be > + * controlled. In this case, the bridge device is a child of the > + * display device and when it will probe it's assured that the display > + * device (and MIPI-DSI host) is present. The display driver will be > + * assured that the bridge driver is connected between the > + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. > + * Therefore, it must run mipi_dsi_host_register() in its probe > + * function, and then run drm_bridge_attach() in its > + * &mipi_dsi_host_ops.attach hook. > + * > + * - The display driver uses the component framework and is a MIPI-DSI > + * host. The bridge device uses the MIPI-DCS commands to be > + * controlled. This is the same situation than above, and can run > + * mipi_dsi_host_register() in either its probe or bind hooks. > + * > + * - The display driver uses the component framework and is a MIPI-DSI > + * host. The bridge device uses a separate bus (such as I2C) to be > + * controlled. In this case, there's no correlation between the probe > + * of the bridge and display drivers, so care must be taken to avoid > + * an endless EPROBE_DEFER loop, with each driver waiting for the > + * other to probe. > + * > + * The ideal pattern to cover the last item (and all the others in the > + * display driver case) is to split the operations like this: > + * > + * - In the display driver must run mipi_dsi_host_register() and > + * component_add in its probe hook. It will make sure that the > + * MIPI-DSI host sticks around, and that the driver's bind can be > + * called. > + * > + * - In its probe hook, the bridge driver must not try to find its > + * MIPI-DSI host or register as a MIPI-DSI device. As far as the > + * framework is concerned, it must only call drm_bridge_add(). > + * > + * - In its bind hook, the display driver must try to find the bridge > + * and return -EPROBE_DEFER if it doesn't find it. If it's there, it > + * must call drm_bridge_attach(). The MIPI-DSI host is now functional. > + * > + * - In its &drm_bridge_funcs.attach hook, the bridge driver can now try > + * to find its MIPI-DSI host and can register as a MIPI-DSI device. > + * > + * At this point, we're now certain that both the display driver and the > + * bridge driver are functional and we can't have a deadlock-like > + * situation when probing. > + */ > + > static DEFINE_MUTEX(bridge_lock); > static LIST_HEAD(bridge_list); > > -- > 2.31.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch