Re: [PATCH v4] drm/msm/dp: remove fail safe mode related code

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On 26/04/2022 23:04, Kuogee Hsieh wrote:
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.

After review all possibilities methods and as discussed on
https://patchwork.freedesktop.org/patch/483155/, supporting EDID
compliance tests in the driver is quite hacky. As seen with other
vendor drivers, supporting these will be much easier with IGT. Hence
removing all the related fail safe code for it so that no possibility
of circular lock will happen.

======================================================
  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

Changes in v2:
-- re text commit title
-- remove all fail safe mode

Changes in v3:
-- remove dp_panel_add_fail_safe_mode() from dp_panel.h
-- add Fixes

Changes in v4:
--  to=dianders@xxxxxxxxxxxx

Fixes: 8b2c181 ("drm/msm/dp: add fail safe mode outside of event_mutex context")
Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>

Fixes: f1b47e6a8df8 ("drm/msm/dp: remove fail safe mode related code")
Reported-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

This does not look correct. Your sign-off should be the latest one. Also please recheck the Fixes tags.

---
  drivers/gpu/drm/msm/dp/dp_panel.c | 11 -----------
  1 file changed, 11 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
index f141872..26f4b695 100644
--- a/drivers/gpu/drm/msm/dp/dp_panel.c
+++ b/drivers/gpu/drm/msm/dp/dp_panel.c
@@ -206,17 +206,6 @@ int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
  			rc = -ETIMEDOUT;
  			goto end;
  		}
-
-		/* 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);
-	} else {
-		/* always add fail-safe mode as backup mode */
-		mutex_lock(&connector->dev->mode_config.mutex);
-		drm_add_modes_noedid(connector, 640, 480);
-		mutex_unlock(&connector->dev->mode_config.mutex);
  	}
if (panel->aux_cfg_update_done) {


--
With best wishes
Dmitry



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