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 52BC4C07E9B for ; Tue, 20 Jul 2021 13:53:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B97F61164 for ; Tue, 20 Jul 2021 13:53:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238939AbhGTNMW (ORCPT ); Tue, 20 Jul 2021 09:12:22 -0400 Received: from wnew3-smtp.messagingengine.com ([64.147.123.17]:51857 "EHLO wnew3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238360AbhGTNFL (ORCPT ); Tue, 20 Jul 2021 09:05:11 -0400 Received: from compute6.internal (compute6.nyi.internal [10.202.2.46]) by mailnew.west.internal (Postfix) with ESMTP id 338272B01189; Tue, 20 Jul 2021 09:45:49 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute6.internal (MEProxy); Tue, 20 Jul 2021 09:45:50 -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=+NaTdju2t0dD7 WUYDPfRGagnPcPZI7VtK/pJug5xl9M=; b=Xm46C04+BUYYCyce90M/0U1C8NvwE zVy0EHDEWB48oHuqh4JRg+S7LY3IOqDn3XtfwLRv88LNG3l1CSNnHNRtNE6XWmg9 vr9HJqQEOK5uYOJDMiOykCYma+uuUwfNUzt323K/LbSICv/4jEgpJbsgnRu3ivXC 0dqH5t90XLHB31S6yaPgQ285Rixm50a5ecOWSmTZPJKfEv1JTClGKRheBdBtMOxm QTfL/WQ7yHdylURuP/QddzBnjMeXztRnar27Ma/F6Sm06QwuiH6Zks0PZ4QpxSGs IqEDbBBjQR46v6qbevISR0aRN4S/sbUYJBY/kuFmeoMRNhfn273XvQqNw== 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=+NaTdju2t0dD7WUYDPfRGagnPcPZI7VtK/pJug5xl9M=; b=YLGz+ta/ s69237/770+28VoEKQMbVXJa+zpsroZAOs1HN88fqdjbSIXDPqM4Wv1/Z6BwmSaD Ls1DSjfK63FFRTOePqMJSRjU/QKlhAfq1ExMDs+UCgpbzDxTyl2WuF5/Anu81Ekq i5DVn7WM/pCEYQsCBkzVswVlvEUHFc3agsgf+a65cXA4+bTNMzB2IQ/Phr2RsJLZ pMh3o0l3sWcU3Iiv8utrRwNaO0C3wT1vLE2lEhNw+BGBcZu8+/JSjkF0+nXr9FIX lZ96iweWJ2Jd4Sm7vQhcUDtqwwPW5Dyh/PqJ9a8UHZdp8monb2ZQsV6CD5F0qcQZ /wglXPqsIGtOVA== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvtddrfedvgdeikecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpefhvffufffkofgjfhgggfestdekredtredttdenucfhrhhomhepofgrgihimhgv ucftihhprghrugcuoehmrgigihhmvgestggvrhhnohdrthgvtghhqeenucggtffrrghtth gvrhhnpedvkeelveefffekjefhffeuleetleefudeifeehuddugffghffhffehveevheeh vdenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpehmrg igihhmvgestggvrhhnohdrthgvtghh X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 20 Jul 2021 09:45:46 -0400 (EDT) From: Maxime Ripard To: Robert Foss , Andrzej Hajda , Daniel Vetter , David Airlie , Sam Ravnborg , Maarten Lankhorst , Thomas Zimmermann , Maxime Ripard , Neil Armstrong , Jonas Karlman , Jernej Skrabec , Thierry Reding , Laurent Pinchart Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges Date: Tue, 20 Jul 2021 15:45:19 +0200 Message-Id: <20210720134525.563936-5-maxime@cerno.tech> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210720134525.563936-1-maxime@cerno.tech> References: <20210720134525.563936-1-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 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 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=-16.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 7566BC07E95 for ; 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Tue, 20 Jul 2021 09:45:46 -0400 (EDT) From: Maxime Ripard To: Robert Foss , Andrzej Hajda , Daniel Vetter , David Airlie , Sam Ravnborg , Maarten Lankhorst , Thomas Zimmermann , Maxime Ripard , Neil Armstrong , Jonas Karlman , Jernej Skrabec , Thierry Reding , Laurent Pinchart Subject: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges Date: Tue, 20 Jul 2021 15:45:19 +0200 Message-Id: <20210720134525.563936-5-maxime@cerno.tech> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210720134525.563936-1-maxime@cerno.tech> References: <20210720134525.563936-1-maxime@cerno.tech> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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 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