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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B4D56CCA471 for ; Fri, 3 Oct 2025 10:39:47 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9B36410E328; Fri, 3 Oct 2025 10:39:44 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=bootlin.com header.i=@bootlin.com header.b="upwAZc38"; dkim-atps=neutral Received: from smtpout-03.galae.net (smtpout-03.galae.net [185.246.85.4]) by gabe.freedesktop.org (Postfix) with ESMTPS id 0A43610E091 for ; Fri, 3 Oct 2025 10:39:43 +0000 (UTC) Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-03.galae.net (Postfix) with ESMTPS id AF14F4E40E90; Fri, 3 Oct 2025 10:39:41 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 84F6760683; Fri, 3 Oct 2025 10:39:41 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 12F32102F1C67; Fri, 3 Oct 2025 12:39:38 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1759487980; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=Qfu3JgcIsjrYY7+XbEdTvSNI3rVgt39kSDML/1Ac/9c=; b=upwAZc38H/sjoI9c8mcboj6oeXPAJsQPew3TzYvjqR+/+DCQJwSLAKqGKNyNWl756zzr49 szwqN8H2FHqMLIev5WxWCl6dT+Wwz6ciHofzvk1iB8weZj+lBuM0NmH+ws2oFdnYk/j7BN HzNerP9hTrCEbPd7JD5cpY7FUpMnRL358Z9SYCmjyZg+wK7ZYh2vvFzrRbpLplUIbSpFur TAAQfT9x6VmEUUTX4ZESiiqEW1o3inCegiUwVczkpuU1YdHUfhC6fkp64ocqe4fpPb87iX PAp5jgCBjTqcovr1HSJPLjoOFNCjjSdXH33jTGxuDYlJRKsGCSGugzpZotDUxg== From: Luca Ceresoli Date: Fri, 03 Oct 2025 12:39:23 +0200 Subject: [PATCH v2 1/7] drm/encoder: add mutex to protect the bridge chain MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251003-drm-bridge-alloc-encoder-chain-mutex-v2-1-78bf61580a06@bootlin.com> References: <20251003-drm-bridge-alloc-encoder-chain-mutex-v2-0-78bf61580a06@bootlin.com> In-Reply-To: <20251003-drm-bridge-alloc-encoder-chain-mutex-v2-0-78bf61580a06@bootlin.com> To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec Cc: Hui Pu , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Luca Ceresoli X-Mailer: b4 0.14.2 X-Last-TLS-Session-Version: TLSv1.3 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" The per-encoder bridge chain is currently assumed to be static once it is fully initialized. Work is in progress to add hot-pluggable bridges, breaking that assumption. With bridge removal, the encoder chain can change without notice, removing tail bridges. This can be problematic while iterating over the chain. Add a mutex to be taken whenever looping or changing the encoder chain. Also add two APIs to lock/unlock the mutex without the need to manipulate internal struct drm_encoder fields. Signed-off-by: Luca Ceresoli --- Changes in v2: - Added documentation to new APIs --- drivers/gpu/drm/drm_encoder.c | 2 ++ include/drm/drm_encoder.h | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c index 8f2bc6a28482229fd0b030a1958f87753ad7885f..3261f142baea30c516499d23dbf8d0acf5952cd6 100644 --- a/drivers/gpu/drm/drm_encoder.c +++ b/drivers/gpu/drm/drm_encoder.c @@ -129,6 +129,7 @@ static int __drm_encoder_init(struct drm_device *dev, } INIT_LIST_HEAD(&encoder->bridge_chain); + mutex_init(&encoder->bridge_chain_mutex); list_add_tail(&encoder->head, &dev->mode_config.encoder_list); encoder->index = dev->mode_config.num_encoder++; @@ -202,6 +203,7 @@ void drm_encoder_cleanup(struct drm_encoder *encoder) kfree(encoder->name); list_del(&encoder->head); dev->mode_config.num_encoder--; + mutex_destroy(&encoder->bridge_chain_mutex); memset(encoder, 0, sizeof(*encoder)); } diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h index 977a9381c8ba943b4d3e021635ea14856df8a17d..449281c37e39f67a0037603762f347f5086df983 100644 --- a/include/drm/drm_encoder.h +++ b/include/drm/drm_encoder.h @@ -25,6 +25,7 @@ #include #include +#include #include #include #include @@ -189,6 +190,9 @@ struct drm_encoder { */ struct list_head bridge_chain; + /** @bridge_chain_mutex: protect bridge_chain from changes while iterating */ + struct mutex bridge_chain_mutex; + const struct drm_encoder_funcs *funcs; const struct drm_encoder_helper_funcs *helper_private; @@ -319,6 +323,41 @@ static inline struct drm_encoder *drm_encoder_find(struct drm_device *dev, return mo ? obj_to_encoder(mo) : NULL; } +/** + * drm_encoder_chain_lock - lock the encoder bridge chain + * @encoder: encoder whose bridge chain must be locked + * + * Locks the mutex protecting the bridge chain from concurrent access. + * To be called by code modifying ot iterating over the bridge chain to + * prevent the list from changing while iterating over it. + * Call drm_encoder_chain_unlock() when done to unlock the mutex. + * + * Returns: + * Pointer to @encoder. Useful to lock the chain and then operate on the + * in the same statement, e.g.: + * list_first_entry_or_null(&drm_encoder_chain_lock(encoder)->bridge_chain) + */ +static inline struct drm_encoder *drm_encoder_chain_lock(struct drm_encoder *encoder) +{ + if (!WARN_ON_ONCE(!encoder)) + mutex_lock(&encoder->bridge_chain_mutex); + + return encoder; +} + +/** + * drm_encoder_chain_unlock - unlock the encoder bridge chain + * @encoder: encoder whose bridge chain must be unlocked + * + * Unlocks the mutex protecting the bridge chain from concurrent access, + * matching drm_encoder_chain_lock(). + */ +static inline void drm_encoder_chain_unlock(struct drm_encoder *encoder) +{ + if (!WARN_ON_ONCE(!encoder)) + mutex_unlock(&encoder->bridge_chain_mutex); +} + void drm_encoder_cleanup(struct drm_encoder *encoder); /** -- 2.51.0