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,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 34647C432BE for ; Thu, 5 Aug 2021 12:19:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D48961102 for ; Thu, 5 Aug 2021 12:19:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239699AbhHEMTq (ORCPT ); Thu, 5 Aug 2021 08:19:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40512 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232808AbhHEMTo (ORCPT ); Thu, 5 Aug 2021 08:19:44 -0400 Received: from mail-ed1-x530.google.com (mail-ed1-x530.google.com [IPv6:2a00:1450:4864:20::530]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B568C061765 for ; Thu, 5 Aug 2021 05:19:29 -0700 (PDT) Received: by mail-ed1-x530.google.com with SMTP id ec13so8133382edb.0 for ; Thu, 05 Aug 2021 05:19:29 -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=CbCDXu5F8o2pipEqw/ORWrNWtlk7d/lKZiGIharZTQM=; b=kM2TkqugolbKb2wWPw/UbONB57ocZI7YH4TyRJ2eXd2RFOwvDyGNqHNPmL5WPy2V80 Uxhi1O2dCD6R38Z/tgApAWKKjjz8zNWMcgsYfsEuGeYU2wUDy7mxypU54CVC7Wp2cLqo b7CeGV1+LMABJ696DiURwEASBQiLvOmr753iw= 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=CbCDXu5F8o2pipEqw/ORWrNWtlk7d/lKZiGIharZTQM=; b=gTNunz/xabFtn/F4x6Dsujlqu1hqtJPRHXYRsWot4Xcx1BAU1lgfc0O5+8RelGiDaB 7UQJisBbO7ojncbswUMCV08zJcF4TxoD3g/D1tFyFvwF+o/4U0KHyvnN9lvlQQOV08dL fOuw8V8Ciyx/kBoqp3/a7NITz7fXwILY62S+E+pNpp9WIXd4QOVuyqJpdlmck9Gv1W2n wqtOAYlnDlFozqQoi+wsGAFI/RMo1xBPcoDrARmUsoYAz8G0+XbwGzzprYM/V1nSE076 63eT76XCkJrUafJF2f5m78xQZx/30Vnt56udd2TTVUfXwLMS2uMM9PJg6B1cKrmzrzSd ro+g== X-Gm-Message-State: AOAM531DFO3p8M9Rj+K6v8ScBqcz2q3ePXrBLhuWoR+wxZUMoSkRJoeo viLV8ZtNJrIYDu75tp8j0wESU/WnXgnwkErYYNiFQA== X-Google-Smtp-Source: ABdhPJyP0Qv/iLG1/KORL16r4bbOe3/ozpue/t2zcmGeQVqgFJTrdQdJ/+AMBerjj1wQuO5M31Lo7Pu2+oKsAxA4/Bc= X-Received: by 2002:a05:6402:cab:: with SMTP id cn11mr6050890edb.369.1628165967971; Thu, 05 Aug 2021 05:19:27 -0700 (PDT) MIME-Version: 1.0 References: <20210720134525.563936-1-maxime@cerno.tech> <20210720134525.563936-5-maxime@cerno.tech> <20210728133531.yzamhx5fhrofxwee@gilmour> In-Reply-To: <20210728133531.yzamhx5fhrofxwee@gilmour> From: Jagan Teki Date: Thu, 5 Aug 2021 17:49:16 +0530 Message-ID: Subject: Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges 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 , dri-devel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Maxime, On Wed, Jul 28, 2021 at 7:05 PM Maxime Ripard wrote: > > Hi Jagan, > > On Tue, Jul 27, 2021 at 03:12:09PM +0530, Jagan Teki wrote: > > 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. > > I'm not really sure what you mean, but if you mention the code we have > in the DSI driver to make sure we can probe without our panel, then it's > not something that we really can support. Bridges cannot be hotplugged > in DRM and having some inconsistencies between drivers (since none of > them behave the same way there) and between what's plugged on the other > side of the DSI bus feels weird. Yes, but for associated bridges to attach on component base DSI drivers the panel_bridge or bridge pointer look necessary. Here is the pseudo code for sun6i_mipi_dsi which support the DSI probe without panel, by waiting for drm pointer to found, but the same seems not possible for bridge cases. static int sun6i_dsi_bridge_attach(struct drm_bridge *bridge, enum drm_bridge_attach_flags flags) { return drm_bridge_attach(bridge->encoder, dsi->bridge, bridge, flags); } static int sun6i_dsi_attach(struct mipi_dsi_host *host, struct mipi_dsi_device *device) { ... if (!dsi->drm || !dsi->drm->registered) return -EPROBE_DEFER; panel = of_drm_find_panel(device->dev.of_node); if (IS_ERR(panel)) { panel = NULL; bridge = of_drm_find_bridge(device->dev.of_node); if (IS_ERR(bridge)) { dev_err(dsi->dev, "failed to find bridge\n"); return PTR_ERR(bridge); } } else { bridge = NULL; } dsi->panel = panel; dsi->bridge = bridge; .... } static int sun6i_dsi_bind(struct device *dev, struct device *master, void *data) { ... ret = drm_bridge_attach(&dsi->encoder, dsi->bridge, NULL, 0); .. dsi->drm = drm; } I believe some-sort bridge handling in hotpulg would necessary to keep the hotplug probing happens for bridge pointers as well. Thanks, Jagan. 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=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 90088C4338F for ; Thu, 5 Aug 2021 12:19:32 +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 9E27A61131 for ; Thu, 5 Aug 2021 12:19:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 9E27A61131 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 C3F086E85A; Thu, 5 Aug 2021 12:19:30 +0000 (UTC) Received: from mail-ed1-x52e.google.com (mail-ed1-x52e.google.com [IPv6:2a00:1450:4864:20::52e]) by gabe.freedesktop.org (Postfix) with ESMTPS id 826536E85A for ; Thu, 5 Aug 2021 12:19:29 +0000 (UTC) Received: by mail-ed1-x52e.google.com with SMTP id x14so8030020edr.12 for ; Thu, 05 Aug 2021 05:19:29 -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=CbCDXu5F8o2pipEqw/ORWrNWtlk7d/lKZiGIharZTQM=; b=kM2TkqugolbKb2wWPw/UbONB57ocZI7YH4TyRJ2eXd2RFOwvDyGNqHNPmL5WPy2V80 Uxhi1O2dCD6R38Z/tgApAWKKjjz8zNWMcgsYfsEuGeYU2wUDy7mxypU54CVC7Wp2cLqo b7CeGV1+LMABJ696DiURwEASBQiLvOmr753iw= 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=CbCDXu5F8o2pipEqw/ORWrNWtlk7d/lKZiGIharZTQM=; b=C0vL/SI88iaCQwq6RUiC3TZPRaLjuyB7o/YxNfalvmUdw6+lZ23jvSqqMEiyVVQPwL 1a8qt/t/O1BkA0aWnm00LSyUZ4TLqfRTbiJjc85v7sxKZpfrMnapo26FeOLusFkMItxB TXTAW45RNU1UxB7x6jlrRk/5/JMtagwOlNe3nlqfHQd0rcGdzctLZjhvEDdtv2XIaxG3 n6h1xJPP0XwLoUPIcpwwRt4UJz9gWVzh0gbvpJvq0uOdXOOU17rjoxdyUvQvzxSxv7Lz bZ6zW0d5tN8sr3eDHmzya7Qs+VIyMZePtNwzi+PuNkuUeayT+Mk6DvURXdV6V9pTjCQG jkzw== X-Gm-Message-State: AOAM530yGrco8KlEmFCHz8zZu3Jt2mWrsm8qLfl+oV0wa6fpYd44XR0f kYFhHpgM0OP4B1wMSYX+K+iBFpBS4i0tDzZi7eoxYA== X-Google-Smtp-Source: ABdhPJyP0Qv/iLG1/KORL16r4bbOe3/ozpue/t2zcmGeQVqgFJTrdQdJ/+AMBerjj1wQuO5M31Lo7Pu2+oKsAxA4/Bc= X-Received: by 2002:a05:6402:cab:: with SMTP id cn11mr6050890edb.369.1628165967971; Thu, 05 Aug 2021 05:19:27 -0700 (PDT) MIME-Version: 1.0 References: <20210720134525.563936-1-maxime@cerno.tech> <20210720134525.563936-5-maxime@cerno.tech> <20210728133531.yzamhx5fhrofxwee@gilmour> In-Reply-To: <20210728133531.yzamhx5fhrofxwee@gilmour> From: Jagan Teki Date: Thu, 5 Aug 2021 17:49:16 +0530 Message-ID: Subject: Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges 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 , dri-devel 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: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Maxime, On Wed, Jul 28, 2021 at 7:05 PM Maxime Ripard wrote: > > Hi Jagan, > > On Tue, Jul 27, 2021 at 03:12:09PM +0530, Jagan Teki wrote: > > 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. > > I'm not really sure what you mean, but if you mention the code we have > in the DSI driver to make sure we can probe without our panel, then it's > not something that we really can support. Bridges cannot be hotplugged > in DRM and having some inconsistencies between drivers (since none of > them behave the same way there) and between what's plugged on the other > side of the DSI bus feels weird. Yes, but for associated bridges to attach on component base DSI drivers the panel_bridge or bridge pointer look necessary. Here is the pseudo code for sun6i_mipi_dsi which support the DSI probe without panel, by waiting for drm pointer to found, but the same seems not possible for bridge cases. static int sun6i_dsi_bridge_attach(struct drm_bridge *bridge, enum drm_bridge_attach_flags flags) { return drm_bridge_attach(bridge->encoder, dsi->bridge, bridge, flags); } static int sun6i_dsi_attach(struct mipi_dsi_host *host, struct mipi_dsi_device *device) { ... if (!dsi->drm || !dsi->drm->registered) return -EPROBE_DEFER; panel = of_drm_find_panel(device->dev.of_node); if (IS_ERR(panel)) { panel = NULL; bridge = of_drm_find_bridge(device->dev.of_node); if (IS_ERR(bridge)) { dev_err(dsi->dev, "failed to find bridge\n"); return PTR_ERR(bridge); } } else { bridge = NULL; } dsi->panel = panel; dsi->bridge = bridge; .... } static int sun6i_dsi_bind(struct device *dev, struct device *master, void *data) { ... ret = drm_bridge_attach(&dsi->encoder, dsi->bridge, NULL, 0); .. dsi->drm = drm; } I believe some-sort bridge handling in hotpulg would necessary to keep the hotplug probing happens for bridge pointers as well. Thanks, Jagan.