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Sat, 07 Nov 2026 17:07:24 -0800 (PST) Received: from DESKTOP-NM9EKIA ([125.134.240.130]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-37265c06c61sm1344623eec.14.2026.11.07.17.07.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Nov 2026 17:07:24 -0800 (PST) From: Joonhoe Kim <26rote@gmail.com> To: Yongxing Mou Cc: sashiko-reviews@lists.linux.dev, Rob Clark , Dmitry Baryshkov , Abhinav Kumar , Sean Paul , Marijn Suijten , David Airlie , Simona Vetter , Jessica Zhang , Dmitry Baryshkov , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 32/35] drm/msm/dp: mark the SST connector disconnected when MST is enabled Date: Sun, 8 Nov 2026 10:07:24 +0900 Message-ID: <20261108010724.4061-1-26rote@gmail.com> X-Mailer: git-send-email 2.55.0.windows.5 In-Reply-To: <20260929045429.A51801F00893@smtp.kernel.org> References: <20260929-msm-dp-mst-v7-0-4b81473185e7@oss.qualcomm.com> <20260929-msm-dp-mst-v7-32-4b81473185e7@oss.qualcomm.com> <20260929045429.A51801F00893@smtp.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Tue, 29 Sep 2026 04:54:29 +0000, sashiko-bot@kernel.org wrote: > Does this introduce an AB-BA deadlock between mode_config.mutex and > plugged_lock? Yes, I hit it on the Lenovo Y700 Gen 5 (TB323FU, Kaanapali) when booting with an MST monitor on the USB-C port (Linux v7.3 with Dmitry's "drm: handle IRQ_HPD events correctly" v8 [1] and this series). The lock order is the same in v7 as posted; nothing in my tree changes it. The HPD worker holds plugged_lock and waits for mode_config.mutex (msm_dp_display_mst_enable() is inlined into msm_dp_display_process_hpd_high()), and the compositor's GETCONNECTOR holds mode_config.mutex and waits for plugged_lock: INFO: task kworker/0:0:9 is blocked on a mutex likely owned by task :2439. INFO: task :2439 is blocked on a mutex likely owned by task kworker/0:0:9. Workqueue: events_freezable pmic_glink_altmode_worker mutex_lock+0x30/0x70 msm_dp_display_process_hpd_high+0x23c/0x2c8 msm_dp_hpd_plug_handle+0xf4/0x208 msm_dp_bridge_hpd_notify+0x118/0x290 drm_bridge_connector_hpd_notify+0x7c/0xf0 drm_bridge_connector_handle_hpd+0x5c/0xc0 drm_bridge_connector_hpd_cb+0x1c/0x30 drm_bridge_hpd_notify_extra+0x4c/0x70 drm_aux_hpd_bridge_notify_extra+0x4c/0x70 pmic_glink_altmode_worker+0x274/0x520 : mutex_lock+0x30/0x70 msm_dp_bridge_detect+0x54/0x338 drm_bridge_connector_detect+0x40/0xc8 drm_helper_probe_single_connector_modes+0x158/0x608 drm_mode_getconnector+0x19c/0x448 32/35 is there to avoid a transient connected -> disconnected change seen by polling. With 25/35, drm_bridge_connector_handle_hpd() stores the result of detect() in connector->status right after hpd_notify() returns, and detect() returns disconnected once mst_active is set (29/35), so I wonder whether the write is still needed. If it is, it could be done without holding plugged_lock. To get past the deadlock I dropped 32/35 locally. Since then, booting with the monitor attached has not hung (4 boots), and over 3 plugs of the monitor with drm.debug=0x4 the SST connector never showed a status change in the probe helper; it stays disconnected while MST is active. [1] https://lore.kernel.org/all/20261024-hpd-irq-events-v8-0-6ee949e7a384@oss.qualcomm.com/ Thanks, Joonhoe Kim