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@chromium.org

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

Fixes: f1b47e6a8df8 ("drm/msm/dp: remove fail safe mode related code") Reported-by: Douglas Anderson dianders@chromium.org

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) {