drm/i915: Prevent modesets during driver init/shutdown

An unexpected modeset or connector detection by a user (user space or FB
console) during the initialization/shutdown sequence is possible either
via a hotplug IRQ handling work or via the connector sysfs
(status/detect) interface. These modesets/detections should be prevented
by disabling/flushing all related hotplug handling work and
unregistering the interfaces that can start them at the beginning of the
shutdown sequence. Some of this - disabling all related intel_hotplug
work - will be done by the next patch, but others - for instance
disabling the MST hotplug works - require a bigger rework.

It makes sense - for diagnostic purpose, even with all the above work and
interface disabled - to detect and reject any such user access. This
patch does that for modeset accesses and a follow-up patch for connector
detection.

During driver loading/unloading/system suspend/shutdown and during
system resume after calling intel_display_driver_disable_user_access()
or intel_display_driver_resume_access() correspondigly, the current
thread is allowed to modeset (as this thread requires to do an
initial/restoring modeset or a disabling modeset), other threads (the
user threads) are not allowed to modeset.

During driver loading/system resume after calling
intel_display_driver_enable_user_access() all threads are allowed to
modeset.

During driver unloading/system suspend/shutdown after calling
intel_display_driver_suspend_access() no threads are allowed to modeset
(as the HW got disabled and should stay in this state).

v2: Call intel_display_driver_suspend_access()/resume_access() only
    for HAS_DISPLAY(). (CI)
v3: (Jouni)
- Add commit log comments explaining how the permission of modeset
  changes during HW init/deinit wrt. to the current and other user
  processes.

Link: https://patchwork.freedesktop.org/patch/msgid/20240104132335.2766434-1-imre.deak@intel.com
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
index 8005a29e78ca..7603771ae107 100644
--- a/drivers/gpu/drm/i915/i915_driver.c
+++ b/drivers/gpu/drm/i915/i915_driver.c
@@ -1005,6 +1005,7 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
 	intel_fbdev_set_suspend(&i915->drm, FBINFO_STATE_SUSPENDED, true);
 	if (HAS_DISPLAY(i915)) {
 		drm_kms_helper_poll_disable(&i915->drm);
+		intel_display_driver_disable_user_access(i915);
 
 		drm_atomic_helper_shutdown(&i915->drm);
 	}
@@ -1014,6 +1015,9 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
 	intel_runtime_pm_disable_interrupts(i915);
 	intel_hpd_cancel_work(i915);
 
+	if (HAS_DISPLAY(i915))
+		intel_display_driver_suspend_access(i915);
+
 	intel_suspend_encoders(i915);
 	intel_shutdown_encoders(i915);
 
@@ -1081,8 +1085,10 @@ static int i915_drm_suspend(struct drm_device *dev)
 	 * properly. */
 	intel_power_domains_disable(dev_priv);
 	intel_fbdev_set_suspend(dev, FBINFO_STATE_SUSPENDED, true);
-	if (HAS_DISPLAY(dev_priv))
+	if (HAS_DISPLAY(dev_priv)) {
 		drm_kms_helper_poll_disable(dev);
+		intel_display_driver_disable_user_access(dev_priv);
+	}
 
 	pci_save_state(pdev);
 
@@ -1093,6 +1099,9 @@ static int i915_drm_suspend(struct drm_device *dev)
 	intel_runtime_pm_disable_interrupts(dev_priv);
 	intel_hpd_cancel_work(dev_priv);
 
+	if (HAS_DISPLAY(dev_priv))
+		intel_display_driver_suspend_access(dev_priv);
+
 	intel_suspend_encoders(dev_priv);
 
 	/* Must be called before GGTT is suspended. */
@@ -1242,14 +1251,20 @@ static int i915_drm_resume(struct drm_device *dev)
 	intel_display_driver_init_hw(dev_priv);
 
 	intel_clock_gating_init(dev_priv);
+
+	if (HAS_DISPLAY(dev_priv))
+		intel_display_driver_resume_access(dev_priv);
+
 	intel_hpd_init(dev_priv);
 
 	/* MST sideband requires HPD interrupts enabled */
 	intel_dp_mst_resume(dev_priv);
 	intel_display_driver_resume(dev_priv);
 
-	if (HAS_DISPLAY(dev_priv))
+	if (HAS_DISPLAY(dev_priv)) {
+		intel_display_driver_enable_user_access(dev_priv);
 		drm_kms_helper_poll_enable(dev);
+	}
 	intel_hpd_poll_disable(dev_priv);
 
 	intel_opregion_resume(dev_priv);