1 files changed, 85 insertions, 0 deletions
diff --git a/debian/patches-rt/0004-drm-i915-Don-t-disable-interrupts-on-PREEMPT_RT-duri.patch b/debian/patches-rt/0004-drm-i915-Don-t-disable-interrupts-on-PREEMPT_RT-duri.patch
new file mode 100644
index 0000000000..9c386e5188
--- /dev/null
+++ b/debian/patches-rt/0004-drm-i915-Don-t-disable-interrupts-on-PREEMPT_RT-duri.patch
@@ -0,0 +1,85 @@
+From: Mike Galbraith <umgwanakikbuti@gmail.com>
+Date: Sat, 27 Feb 2016 09:01:42 +0100
+Subject: [PATCH 04/10] drm/i915: Don't disable interrupts on PREEMPT_RT during
+ atomic updates
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
+
+Commit
+   8d7849db3eab7 ("drm/i915: Make sprite updates atomic")
+
+started disabling interrupts across atomic updates. This breaks on PREEMPT_RT
+because within this section the code attempt to acquire spinlock_t locks which
+are sleeping locks on PREEMPT_RT.
+
+According to the comment the interrupts are disabled to avoid random delays and
+not required for protection or synchronisation.
+If this needs to happen with disabled interrupts on PREEMPT_RT, and the
+whole section is restricted to register access then all sleeping locks
+need to be acquired before interrupts are disabled and some function
+maybe moved after enabling interrupts again.
+This includes:
+- prepare_to_wait() + finish_wait() due its wake queue.
+- drm_crtc_vblank_put() -> vblank_disable_fn() drm_device::vbl_lock.
+- skl_pfit_enable(), intel_update_plane(), vlv_atomic_update_fifo() and
+  maybe others due to intel_uncore::lock
+- drm_crtc_arm_vblank_event() due to drm_device::event_lock and
+  drm_device::vblank_time_lock.
+
+Don't disable interrupts on PREEMPT_RT during atomic updates.
+
+[bigeasy: drop local locks, commit message]
+
+Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ drivers/gpu/drm/i915/display/intel_crtc.c |   15 ++++++++++-----
+ 1 file changed, 10 insertions(+), 5 deletions(-)
+
+--- a/drivers/gpu/drm/i915/display/intel_crtc.c
++++ b/drivers/gpu/drm/i915/display/intel_crtc.c
+@@ -534,7 +534,8 @@ void intel_pipe_update_start(struct inte
+ 	 */
+ 	intel_psr_wait_for_idle_locked(new_crtc_state);
+ 
+-	local_irq_disable();
++	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
++		local_irq_disable();
+ 
+ 	crtc->debug.min_vbl = min;
+ 	crtc->debug.max_vbl = max;
+@@ -559,11 +560,13 @@ void intel_pipe_update_start(struct inte
+ 			break;
+ 		}
+ 
+-		local_irq_enable();
++		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
++			local_irq_enable();
+ 
+ 		timeout = schedule_timeout(timeout);
+ 
+-		local_irq_disable();
++		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
++			local_irq_disable();
+ 	}
+ 
+ 	finish_wait(wq, &wait);
+@@ -596,7 +599,8 @@ void intel_pipe_update_start(struct inte
+ 	return;
+ 
+ irq_disable:
+-	local_irq_disable();
++	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
++		local_irq_disable();
+ }
+ 
+ #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_VBLANK_EVADE)
+@@ -706,7 +710,8 @@ void intel_pipe_update_end(struct intel_
+ 		intel_crtc_update_active_timings(new_crtc_state,
+ 						 new_crtc_state->vrr.enable);
+ 
+-	local_irq_enable();
++	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
++		local_irq_enable();
+ 
+ 	if (intel_vgpu_active(dev_priv))
+ 		return;