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=-18.8 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,URIBL_BLOCKED, USER_AGENT_GIT 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 288D0C4338F for ; Wed, 28 Jul 2021 13:32:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13EB960FED for ; Wed, 28 Jul 2021 13:32:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236465AbhG1Ncx (ORCPT ); Wed, 28 Jul 2021 09:32:53 -0400 Received: from new3-smtp.messagingengine.com ([66.111.4.229]:48319 "EHLO new3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236425AbhG1Nct (ORCPT ); Wed, 28 Jul 2021 09:32:49 -0400 Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailnew.nyi.internal (Postfix) with ESMTP id C5F51580B89; Wed, 28 Jul 2021 09:32:47 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute4.internal (MEProxy); Wed, 28 Jul 2021 09:32:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cerno.tech; h= from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; s=fm3; bh=n2kX7j4p1fO2w 1C+PjBmTewZIHMsxhZO45DlOqT2O4Y=; b=FDX+ngQH8N4rCBmz4gqGHwPV4SW// 9cXnitKdLnWUNjUANU/0DFSffUvHxRQpu8LPIzVWZEV4Hc5xaTgy80S3t+aW6OVy CX06IMDzhJt7QYCpMAopYm+oa0SfXDWWgw6hPYQL2cyCzB6sOxPSllqrLnBDCSNV yh0vlo/20ovtbzWJOojlhADKHYEcPNbSr5FJIWR6wd6Xr86iu182mkosLnFnwPIe BIOP2WGc7y+tKpH3b7r9qBtNcU7Mjw7xHn37Uqb2k/hOoRWnhFD9tChSFCxOUNUQ ujsfL5L9UJ0tQQbzI1eJ5hT5txpOu4YM9iWB+ud+JNsH1+wvu7+g8Qtrw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm3; bh=n2kX7j4p1fO2w1C+PjBmTewZIHMsxhZO45DlOqT2O4Y=; b=UrZohK23 +Xzrh+zEk6e7cAJkwoDMY02R9L7aLmdkjcpfnHAgyElkn3FmDwNCr/R3p5V0JMWD 6JwG0zGsa93g2CD/ZWpZcwIBB5zwGVbuEYaA/9ZZ34lG80WGdKgAmaysJ3UvQZ4n 86gYyRAoPSHDuJwP7x7bfT/bLD0+rvFZVwSceucQQIeGVdTQNvspJ0Qx3rf3Jyc7 ax/UNi48c7uvJTc4OfSTtA3APmg/Ot6CBE8W9S4QMQmdNoTyPI+9tVHJGD3VeNW/ YUjbCZcOyiZdibbVdaER1yxgCtqdZW/+CmMmTYpzbT1ENwXBbaM+6OWmraQdCwdS wCF8P+NCpzahZQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvtddrgeelgdeivdcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpefhvffufffkofgjfhgggfestdekredtredttdenucfhrhhomhepofgrgihimhgv ucftihhprghrugcuoehmrgigihhmvgestggvrhhnohdrthgvtghhqeenucggtffrrghtth gvrhhnpedvkeelveefffekjefhffeuleetleefudeifeehuddugffghffhffehveevheeh vdenucevlhhushhtvghrufhiiigvpedvnecurfgrrhgrmhepmhgrihhlfhhrohhmpehmrg igihhmvgestggvrhhnohdrthgvtghh X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 28 Jul 2021 09:32:47 -0400 (EDT) From: Maxime Ripard To: Sam Ravnborg , Daniel Vetter , David Airlie , Thierry Reding , Laurent Pinchart , Maarten Lankhorst , Thomas Zimmermann , Maxime Ripard , Jernej Skrabec , Neil Armstrong , Andrzej Hajda , Jonas Karlman , Robert Foss Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH v2 4/8] drm/bridge: Document the probe issue with MIPI-DSI bridges Date: Wed, 28 Jul 2021 15:32:25 +0200 Message-Id: <20210728133229.2247965-5-maxime@cerno.tech> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210728133229.2247965-1-maxime@cerno.tech> References: <20210728133229.2247965-1-maxime@cerno.tech> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 71d3370ce209..fd01f1ce7976 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -94,6 +94,66 @@ * 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