[Freedreno] [PATCH] drm/msm/dp: move add fail safe mode to dp_connector_get_mode()

Kuogee Hsieh quic_khsieh at quicinc.com
Fri Apr 22 23:45:23 UTC 2022 

Current DP driver implementation has adding safe mode done at
dp_hpd_plug_handle() which is expected to be executed under event
thread context.

However there is possible circular locking happen (see blow stack trace)
after edp driver call dp_hpd_plug_handle() from dp_bridge_enable() which
is executed under drm_thread context.

To break this circular locking, this patch have safe mode added at
dp_connector_get_mode() which is executed under drm thread context.
Therefore no lock acquired required for &dev->mode_config.mutex while
adding fail safe mode since it has been hold by drm thread already.

======================================================
 WARNING: possible circular locking dependency detected
 5.15.35-lockdep #6 Tainted: G        W
 ------------------------------------------------------
 frecon/429 is trying to acquire lock:
 ffffff808dc3c4e8 (&dev->mode_config.mutex){+.+.}-{3:3}, at:
dp_panel_add_fail_safe_mode+0x4c/0xa0

 but task is already holding lock:
 ffffff808dc441e0 (&kms->commit_lock[i]){+.+.}-{3:3}, at: lock_crtcs+0xb4/0x124

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #3 (&kms->commit_lock[i]){+.+.}-{3:3}:
        __mutex_lock_common+0x174/0x1a64
        mutex_lock_nested+0x98/0xac
        lock_crtcs+0xb4/0x124
        msm_atomic_commit_tail+0x330/0x748
        commit_tail+0x19c/0x278
        drm_atomic_helper_commit+0x1dc/0x1f0
        drm_atomic_commit+0xc0/0xd8
        drm_atomic_helper_set_config+0xb4/0x134
        drm_mode_setcrtc+0x688/0x1248
        drm_ioctl_kernel+0x1e4/0x338
        drm_ioctl+0x3a4/0x684
        __arm64_sys_ioctl+0x118/0x154
        invoke_syscall+0x78/0x224
        el0_svc_common+0x178/0x200
        do_el0_svc+0x94/0x13c
        el0_svc+0x5c/0xec
        el0t_64_sync_handler+0x78/0x108
        el0t_64_sync+0x1a4/0x1a8

 -> #2 (crtc_ww_class_mutex){+.+.}-{3:3}:
        __mutex_lock_common+0x174/0x1a64
        ww_mutex_lock+0xb8/0x278
        modeset_lock+0x304/0x4ac
        drm_modeset_lock+0x4c/0x7c
        drmm_mode_config_init+0x4a8/0xc50
        msm_drm_init+0x274/0xac0
        msm_drm_bind+0x20/0x2c
        try_to_bring_up_master+0x3dc/0x470
        __component_add+0x18c/0x3c0
        component_add+0x1c/0x28
        dp_display_probe+0x954/0xa98
        platform_probe+0x124/0x15c
        really_probe+0x1b0/0x5f8
        __driver_probe_device+0x174/0x20c
        driver_probe_device+0x70/0x134
        __device_attach_driver+0x130/0x1d0
        bus_for_each_drv+0xfc/0x14c
        __device_attach+0x1bc/0x2bc
        device_initial_probe+0x1c/0x28
        bus_probe_device+0x94/0x178
        deferred_probe_work_func+0x1a4/0x1f0
        process_one_work+0x5d4/0x9dc
        worker_thread+0x898/0xccc
        kthread+0x2d4/0x3d4
        ret_from_fork+0x10/0x20

 -> #1 (crtc_ww_class_acquire){+.+.}-{0:0}:
        ww_acquire_init+0x1c4/0x2c8
        drm_modeset_acquire_init+0x44/0xc8
        drm_helper_probe_single_connector_modes+0xb0/0x12dc
        drm_mode_getconnector+0x5dc/0xfe8
        drm_ioctl_kernel+0x1e4/0x338
        drm_ioctl+0x3a4/0x684
        __arm64_sys_ioctl+0x118/0x154
        invoke_syscall+0x78/0x224
        el0_svc_common+0x178/0x200
        do_el0_svc+0x94/0x13c
        el0_svc+0x5c/0xec
        el0t_64_sync_handler+0x78/0x108
        el0t_64_sync+0x1a4/0x1a8

 -> #0 (&dev->mode_config.mutex){+.+.}-{3:3}:
        __lock_acquire+0x2650/0x672c
        lock_acquire+0x1b4/0x4ac
        __mutex_lock_common+0x174/0x1a64
        mutex_lock_nested+0x98/0xac
        dp_panel_add_fail_safe_mode+0x4c/0xa0
        dp_hpd_plug_handle+0x1f0/0x280
        dp_bridge_enable+0x94/0x2b8
        drm_atomic_bridge_chain_enable+0x11c/0x168
        drm_atomic_helper_commit_modeset_enables+0x500/0x740
        msm_atomic_commit_tail+0x3e4/0x748
        commit_tail+0x19c/0x278
        drm_atomic_helper_commit+0x1dc/0x1f0
        drm_atomic_commit+0xc0/0xd8
        drm_atomic_helper_set_config+0xb4/0x134
        drm_mode_setcrtc+0x688/0x1248
        drm_ioctl_kernel+0x1e4/0x338
        drm_ioctl+0x3a4/0x684
        __arm64_sys_ioctl+0x118/0x154
        invoke_syscall+0x78/0x224
        el0_svc_common+0x178/0x200
        do_el0_svc+0x94/0x13c
        el0_svc+0x5c/0xec
        el0t_64_sync_handler+0x78/0x108
        el0t_64_sync+0x1a4/0x1a8

Signed-off-by: Kuogee Hsieh <quic_khsieh at quicinc.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c |  6 ------
 drivers/gpu/drm/msm/dp/dp_panel.c   | 23 +++++++++++++----------
 2 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 92cd50f..01453db 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -555,12 +555,6 @@ static int dp_hpd_plug_handle(struct dp_display_private *dp, u32 data)
 
 	mutex_unlock(&dp->event_mutex);
 
-	/*
-	 * add fail safe mode outside event_mutex scope
-	 * to avoid potiential circular lock with drm thread
-	 */
-	dp_panel_add_fail_safe_mode(dp->dp_display.connector);
-
 	/* uevent will complete connection part */
 	return 0;
 };
diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
index 1aa9aa8c..23fee42 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.c
+++ b/drivers/gpu/drm/msm/dp/dp_panel.c
@@ -151,15 +151,6 @@ static int dp_panel_update_modes(struct drm_connector *connector,
 	return rc;
 }
 
-void dp_panel_add_fail_safe_mode(struct drm_connector *connector)
-{
-	/* fail safe edid */
-	mutex_lock(&connector->dev->mode_config.mutex);
-	if (drm_add_modes_noedid(connector, 640, 480))
-		drm_set_preferred_mode(connector, 640, 480);
-	mutex_unlock(&connector->dev->mode_config.mutex);
-}
-
 int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
 	struct drm_connector *connector)
 {
@@ -216,7 +207,11 @@ int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
 			goto end;
 		}
 
-		dp_panel_add_fail_safe_mode(connector);
+		/* fail safe edid */
+		mutex_lock(&connector->dev->mode_config.mutex);
+		if (drm_add_modes_noedid(connector, 640, 480))
+			drm_set_preferred_mode(connector, 640, 480);
+		mutex_unlock(&connector->dev->mode_config.mutex);
 	}
 
 	if (panel->aux_cfg_update_done) {
@@ -266,6 +261,14 @@ int dp_panel_get_modes(struct dp_panel *dp_panel,
 		return -EINVAL;
 	}
 
+	/*
+	 * add fail safe mode (640x480) here
+	 * since we are executed in drm_thread context,
+	 * no mode_config.mutex acquired required
+	 */
+	if (drm_add_modes_noedid(connector, 640, 480))
+		drm_set_preferred_mode(connector, 640, 480);
+
 	if (dp_panel->edid)
 		return dp_panel_update_modes(connector, dp_panel->edid);
 
-- 
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