From a112ba7606a5d2a3b644a51dd847a3e98fbf5226 Mon Sep 17 00:00:00 2001
From: Mike Galbraith <umgwanakikbuti@gmail.com>
Date: Sat, 27 Feb 2016 09:01:42 +0100
Subject: [PATCH 114/158] drm/i915: Don't disable interrupts on PREEMPT_RT
 during atomic updates

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(-)

Index: linux-5.15/drivers/gpu/drm/i915/display/intel_crtc.c
===================================================================
--- linux-5.15.orig/drivers/gpu/drm/i915/display/intel_crtc.c
+++ linux-5.15/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -425,7 +425,8 @@ void intel_pipe_update_start(const struc
 	 */
 	intel_psr_wait_for_idle(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;
@@ -450,11 +451,13 @@ void intel_pipe_update_start(const struc
 			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);
@@ -487,7 +490,8 @@ void intel_pipe_update_start(const struc
 	return;
 
 irq_disable:
-	local_irq_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_disable();
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_VBLANK_EVADE)
@@ -566,7 +570,8 @@ void intel_pipe_update_end(struct intel_
 		new_crtc_state->uapi.event = NULL;
 	}
 
-	local_irq_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_enable();
 
 	/* Send VRR Push to terminate Vblank */
 	intel_vrr_send_push(new_crtc_state);