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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D2A2CC55162 for ; Mon, 3 Aug 2026 01:39:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=hCaqyyISkfmc8KoVMA+IE9BEl7i+kSQyUjrBtfdkvIc=; b=JYEQYX1HyxJssQy+HQhpNXMopV yXaBGGlASwh5QtfM8EnR5FcIZjOrJMRFdfriv59SFKAoEk5CgytNsRNxgg6+cNaeYpIqd2nRFF7gb 7QgfF1qQXWoWbtU6cDkR7IeEVhZFN3YmbsEJ9XtMH6HCZL4lg6kLBzpzW1wFBhbzt+iNlp0eY1Kp5 XglTHvAxQ0jNrHE+jEh5dAErnUh3V6/8weuqIMaFvOH2N/yQ1mqPCV98qZh+Qf0ak32t6M3Ha3vfo X5TzZLEyOLIjlX7BNL3WP5gFR+MbLDuJrqBGzivOzsH2Q2tN7wg/p+VtHaxZPcFub4BYb+6D2UQHZ O8zmuFvA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wqhdk-0000000GALh-48Hi; Mon, 03 Aug 2026 01:38:52 +0000 Received: from mail-m158132.netease.com ([47.251.158.132]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wqhde-0000000GAKb-3KTa; Mon, 03 Aug 2026 01:38:50 +0000 Received: from [127.0.0.1] (unknown [61.154.14.86]) by smtp.qiye.163.com (Hmail) with ESMTP id 487cbd68b; Mon, 3 Aug 2026 09:38:26 +0800 (GMT+08:00) Message-ID: Date: Mon, 3 Aug 2026 09:38:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/6] drm/bridge: Implement generic USB Type-C DP HPD bridge To: Sebastian Reichel Cc: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Sandy Huang , =?UTF-8?Q?Heiko_St=C3=BCbner?= , Andy Yan , Vinod Koul , Nicolas Frattaroli , Heikki Krogerus , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-phy@lists.infradead.org References: <20260730013349.51-1-kernel@airkyi.com> <20260730013349.51-2-kernel@airkyi.com> Content-Language: en-US From: Chaoyi Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-HM-Tid: 0a9fc545af7303a7kunmdf79e4127cbc75 X-HM-MType: 1 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFITzdXWRgWCB1ZQUpXWS1ZQUlXWQ8JGhUIEh9ZQVlCH0hCVhlCSUxCSB5CHx1CHlYVFA kWGhdVEwETFhoSFyQUDg9ZV1kYEgtZQVlNSlVKTk9VSk9VQ01ZV1kWGg8SFR0UWUFZT0tIVUpLSU 9PT0hVSktLVUpCS0tZBg++ DKIM-Signature: a=rsa-sha256; b=Jt5HTmsU9lA0nVJbfxu5LdwAyRIq9ZBtXrW3nIcOVhQXF0H4282MRbkzExrMAbPWV2ZeVjMQYl6mf7ZqUDz8jYEWQLUo/NPo3/7n6w/vYPCXxwIWRW0Tn3FmfFwXuin4YyI0Lqv0nVORUrti9WiKpQkwmAKSxD9cR/jyimtV30o=; s=default; c=relaxed/relaxed; d=rock-chips.com; v=1; bh=hCaqyyISkfmc8KoVMA+IE9BEl7i+kSQyUjrBtfdkvIc=; h=date:mime-version:subject:message-id:from; X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260802_183848_725302_1CA6648F X-CRM114-Status: GOOD ( 38.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Sebastian, On 7/31/2026 10:20 PM, Sebastian Reichel wrote: > Hi, > > On Thu, Jul 30, 2026 at 09:33:44AM +0800, Chaoyi Chen wrote: >> From: Chaoyi Chen >> >> The HPD function of Type-C DP is implemented through >> drm_connector_oob_hotplug_event(). For embedded DP, it is required >> that the DRM connector fwnode corresponds to the Type-C port fwnode. >> >> To describe the relationship between the DP controller and the Type-C >> port device, we usually using drm_bridge to build a bridge chain. >> >> Now several USB-C controller drivers have already implemented the DP >> HPD bridge function provided by aux-hpd-bridge.c, it will build a DP >> HPD bridge on USB-C connector port device. >> >> But this requires the USB-C controller driver to manually register the >> HPD bridge. If the driver does not implement this feature, the bridge >> will not be create. >> >> So this patch implements a generic DP HPD bridge based on >> aux-hpd-bridge.c. It will monitor Type-C bus events, and when a >> Type-C port device containing the DP svid is registered, it will >> create an HPD bridge for it without the need for the USB-C controller >> driver to implement it. >> >> Signed-off-by: Chaoyi Chen >> Reviewed-by: Heikki Krogerus >> Reviewed-by: Nicolas Frattaroli >> --- >> >> (no changes since v5) >> >> Changes in v4: >> - Scan the entire typec_bus and attempt to register the hpd bridge, >> so as not to miss devices that were already added during initialization. >> >> (no changes since v3) >> >> Changes in v2: >> - Add copyright text. >> - Remove useless goto. >> --- >> drivers/gpu/drm/bridge/Kconfig | 10 +++ >> drivers/gpu/drm/bridge/Makefile | 1 + >> .../gpu/drm/bridge/aux-hpd-typec-dp-bridge.c | 64 +++++++++++++++++++ >> 3 files changed, 75 insertions(+) >> create mode 100644 drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c >> >> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig >> index 4a57d49b4c6d..9739b2a19758 100644 >> --- a/drivers/gpu/drm/bridge/Kconfig >> +++ b/drivers/gpu/drm/bridge/Kconfig >> @@ -30,6 +30,16 @@ config DRM_AUX_HPD_BRIDGE >> Simple bridge that terminates the bridge chain and provides HPD >> support. >> >> +if DRM_AUX_HPD_BRIDGE >> +config DRM_AUX_HPD_TYPEC_BRIDGE >> + tristate >> + depends on TYPEC || !TYPEC >> + default TYPEC >> + help >> + Simple bridge that terminates the bridge chain and provides HPD >> + support. It build bridge on each USB-C connector device node. >> +endif >> + >> menu "Display Interface Bridges" >> depends on DRM && DRM_BRIDGE >> >> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile >> index 15cc821d85b7..d88a9e1ccc9a 100644 >> --- a/drivers/gpu/drm/bridge/Makefile >> +++ b/drivers/gpu/drm/bridge/Makefile >> @@ -1,6 +1,7 @@ >> # SPDX-License-Identifier: GPL-2.0 >> obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o >> obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += aux-hpd-bridge.o >> +obj-$(CONFIG_DRM_AUX_HPD_TYPEC_BRIDGE) += aux-hpd-typec-dp-bridge.o >> obj-$(CONFIG_DRM_CHIPONE_ICN6211) += chipone-icn6211.o >> obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o >> obj-$(CONFIG_DRM_CROS_EC_ANX7688) += cros-ec-anx7688.o >> diff --git a/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c >> new file mode 100644 >> index 000000000000..43af3ea20f20 >> --- /dev/null >> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c >> @@ -0,0 +1,64 @@ >> +// SPDX-License-Identifier: GPL-2.0+ >> +/* >> + * Copyright (C) 2026 Rockchip Electronics Co., Ltd. >> + * >> + * Author: Chaoyi Chen >> + */ >> +#include >> +#include >> +#include >> + >> +#include >> + >> +static int drm_typec_bus_event(struct notifier_block *nb, >> + unsigned long action, void *data) >> +{ >> + struct device *dev = (struct device *)data; >> + struct typec_altmode *alt = to_typec_altmode(dev); >> + >> + if (action != BUS_NOTIFY_ADD_DEVICE) >> + return NOTIFY_OK; >> + >> + /* >> + * alt->dev.parent->parent : USB-C controller device >> + * alt->dev.parent : USB-C connector device >> + */ >> + if (is_typec_port_altmode(&alt->dev) && alt->svid == USB_TYPEC_DP_SID) >> + drm_dp_hpd_bridge_register(alt->dev.parent->parent, >> + to_of_node(alt->dev.parent->fwnode)); > > So there are 3 ways to end up with duplicated hpd bridges now: > > 1. TypeC controller driver already registered one manually > 2. There is a race in drm_aux_hpd_typec_dp_bridge_module_init, if a > device appears between registering the notifier and looping > through all pre-existing devices > 3. Reloading the aux-hpd-typec-dp-bridge module re-registers the > bridges > > It's not a huge problem as the system works with the duplicated HPD > bridges, but it's also quite ugly. > > I think it can be trivially avoided by adding this function to > drivers/gpu/drm/bridge/aux-hpd-bridge.c and then making use of it > here as an additional check (code untested): > > bool drm_device_has_dp_hpd_bridge(struct device *parent) > { > struct device *hpd_bridge = device_find_child_by_name(parent, "dp_hpd_bridge"); > > if (!hpd_bridge) > return false; > > put_device(hpd_bridge); > return true; > } > EXPORT_SYMBOL_GPL(drm_dev_has_dp_hpd_bridge); > I think deduplication during registration is a good idea. Detecting it during alloc seems a bit premature. Thanks again for your suggestion. I'll try to add it in the next version. > That would solve all of the above, but leaves one problem when this > module races against manual device creation in a TypeC controller > driver. That could be avoided by doing the check in > devm_drm_dp_hpd_bridge_alloc() under a lock, but that's probably not > worth the trouble (it would require updating all users to handle a > new error code like -EEXIST) considering manual registration can be > removed from all drivers anyways. > > Greetings, > > -- Sebastian > >> + >> + return NOTIFY_OK; >> +} >> + >> +static struct notifier_block drm_typec_event_nb = { >> + .notifier_call = drm_typec_bus_event, >> +}; >> + >> +static int check_device_already_added(struct device *dev, void *data) >> +{ >> + drm_typec_bus_event(NULL, BUS_NOTIFY_ADD_DEVICE, dev); >> + return 0; >> +} >> + >> +static void drm_aux_hpd_typec_dp_bridge_module_exit(void) >> +{ >> + bus_unregister_notifier(&typec_bus, &drm_typec_event_nb); >> +} >> + >> +static int __init drm_aux_hpd_typec_dp_bridge_module_init(void) >> +{ >> + bus_register_notifier(&typec_bus, &drm_typec_event_nb); >> + /* >> + * Before module initialization, some devices may have already been added. >> + * Register the HPD bridge for these devices. >> + */ >> + bus_for_each_dev(&typec_bus, NULL, NULL, check_device_already_added); >> + return 0; >> +} >> + >> +module_init(drm_aux_hpd_typec_dp_bridge_module_init); >> +module_exit(drm_aux_hpd_typec_dp_bridge_module_exit); >> + >> +MODULE_AUTHOR("Chaoyi Chen "); >> +MODULE_DESCRIPTION("DRM TYPEC DP HPD BRIDGE"); >> +MODULE_LICENSE("GPL"); >> -- >> 2.53.0 >> -- Best, Chaoyi