From nobody Wed Dec 17 19:16:26 2025 Received: from smtpout-04.galae.net (smtpout-04.galae.net [185.171.202.116]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3722681720 for ; Fri, 3 Oct 2025 10:39:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.171.202.116 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759487985; cv=none; b=M+F8aKMcWQVp219ko2XeENtizNv3rH8MlbatO6g1ZoAhq2SHVj72y+rIJ6drPLGzy8bnb/NuJdbZZz5bIc+W6sz4IDxmLCGvwoqojPI0Ct1I+VHeJh0Ii60PNB6ewZGxxHdspat9nmM3Y2WZlK+QrAejORcmyc1xyCtq4dmlh/U= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759487985; c=relaxed/simple; bh=KX49EIdCKMoNVJPsWgELjfff+Y5Kp5R86U4uS+ZpzDk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=hYNutGfsQJlGyQQcuspmLNlgd5ELcrSjrm5oKDtV2IIp0mE5NJEYjA9of/ocYENKNqbJ897suVGF11U8vs8r2XqaVy7rxWaieyFfbMIYG+KAo7zf6zOzEbNk4otyTetzkwqI6JzqIltu9vJICsQ5Fzk+x9sjewGEAWxHZtp6OaA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=upwAZc38; arc=none smtp.client-ip=185.171.202.116 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="upwAZc38" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id 85783C00D99; Fri, 3 Oct 2025 10:39:23 +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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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 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..3261f142baea30c516499d23dbf= 8d0acf5952cd6 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, } =20 INIT_LIST_HEAD(&encoder->bridge_chain); + mutex_init(&encoder->bridge_chain_mutex); list_add_tail(&encoder->head, &dev->mode_config.encoder_list); encoder->index =3D dev->mode_config.num_encoder++; =20 @@ -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); =20 memset(encoder, 0, sizeof(*encoder)); } diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h index 977a9381c8ba943b4d3e021635ea14856df8a17d..449281c37e39f67a0037603762f= 347f5086df983 100644 --- a/include/drm/drm_encoder.h +++ b/include/drm/drm_encoder.h @@ -25,6 +25,7 @@ =20 #include #include +#include #include #include #include @@ -189,6 +190,9 @@ struct drm_encoder { */ struct list_head bridge_chain; =20 + /** @bridge_chain_mutex: protect bridge_chain from changes while iteratin= g */ + struct mutex bridge_chain_mutex; + const struct drm_encoder_funcs *funcs; const struct drm_encoder_helper_funcs *helper_private; =20 @@ -319,6 +323,41 @@ static inline struct drm_encoder *drm_encoder_find(str= uct drm_device *dev, return mo ? obj_to_encoder(mo) : NULL; } =20 +/** + * 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_encode= r *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); =20 /** --=20 2.51.0