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=-13.5 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 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 3AE76C432BE for ; Tue, 27 Jul 2021 09:42:24 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5763A6054F for ; Tue, 27 Jul 2021 09:42:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5763A6054F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=amarulasolutions.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D0A516E8FC; Tue, 27 Jul 2021 09:42:22 +0000 (UTC) Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by gabe.freedesktop.org (Postfix) with ESMTPS id CDDA16E8FC for ; Tue, 27 Jul 2021 09:42:21 +0000 (UTC) Received: by mail-ed1-x529.google.com with SMTP id f13so11784363edq.13 for ; Tue, 27 Jul 2021 02:42:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8fwQRqMvjgAY6jqV3zlS3GTvqGBBIFqRUeOfjbqNkn4=; b=Vgfr+F5s6Bc5u+uBdMFEhmPySf4LlqpmA8B3AA57fdSa5RwUSGJbIA6tW/1gVcaXOU Vo7X6tgClf+huAZ2z6IUZubQy5E7JzTpiWc2YEhbw46JuKlohm1vKn3zNdJG5ZAW8UAd UsIMO676lnPLuTnVA+C6Na7p2LQ0GHrw5luy8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=8fwQRqMvjgAY6jqV3zlS3GTvqGBBIFqRUeOfjbqNkn4=; b=UUosxVHuTyXGDGYXLdFg53LYt2aXEPJ73X9uIDCzCREDNyGv5X6acrXNrmdNRc7JGj V/SHixQyxAOpzVgcSC9Re0wTLiGCTgO8m1BHOPmRIkoy0ofOhBFEt5ji8VokB3gvq5tu aTgO6guBINCeQASpmYP9YWkUwHGCglhe11fzdFxIsScMC8pKlmzNbWxUn7+1T3rp/8Gz XJrJfnO4/X6KAAkH2QK+yM9rAc65K9l8TUfFKaoOyR6n/jW3+NmpFlyb+myE6owDYHHE SfWu9eE3MIAjma1r8SKOl3rfOwhWZO1dPay2Zu4FRmBbM/ibA0o/O8OB99/8BrNBTWj9 XflA== X-Gm-Message-State: AOAM530vskO9HjaKniGi0T0HbOK7NdBG8Dk6i7WiugCJiASsf/qJ4Rnb LT2NIqwodlugUS/Sa0GGRU+pHnvtOyCwNsZW1EJteg== X-Google-Smtp-Source: ABdhPJyeCw9Vo5e9UrsFOswe3Y1tnwFbw3IAOf1WcRCfMxjGuFl09sckUW6CTR3uJUSW6D+U6LZrWYW/ZJWeDClExRU= X-Received: by 2002:a05:6402:430b:: with SMTP id m11mr7510996edc.55.1627378940202; Tue, 27 Jul 2021 02:42:20 -0700 (PDT) MIME-Version: 1.0 References: <20210720134525.563936-1-maxime@cerno.tech> <20210720134525.563936-5-maxime@cerno.tech> In-Reply-To: <20210720134525.563936-5-maxime@cerno.tech> From: Jagan Teki Date: Tue, 27 Jul 2021 15:12:09 +0530 Message-ID: Subject: Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges To: Maxime Ripard Content-Type: text/plain; charset="UTF-8" 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: Neil Armstrong , David Airlie , dri-devel , Jonas Karlman , linux-kernel , Robert Foss , Andrzej Hajda , Thierry Reding , Jernej Skrabec , Thomas Zimmermann , Daniel Vetter , Sam Ravnborg , Laurent Pinchart Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, Jul 20, 2021 at 7:15 PM 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 > --- > 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. There is an another problem occur for this scenario in the case of kms hotplug driver, sun6i_mipi_dsi.c. When host attach wait till drm device pointer found and drm device pointer would found only when bind done, and bind would complete only when &drm_bridge_funcs.attach hooks are complete. But, If DSI driver is fully bridge driven then this attach in bind will trigger panel_bridge hook attach and at this point we cannot get panel_bridge at all which indeed second attach would would failed. This is one of the reason I'm trying to use drm_bridge_attach host attach itself instead of component bind, not yet succeeded. Thanks, Jagan.