[SRU][R][Unstable][PATCH 04/12] UBUNTU: SAUCE: drm/i915: Don't disable interrupts on PREEMPT_RT during atomic updates

[Kevin Becker]

From: Mike Galbraith <umgwanakikbuti at gmail.com>

BugLink: https://bugs.launchpad.net/bugs/2143181

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 at gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
Signed-off-by: Kevin Becker <kevin.becker at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_crtc.c   | 9 ++++++---
 drivers/gpu/drm/i915/display/intel_cursor.c | 9 ++++++---
 drivers/gpu/drm/i915/display/intel_vblank.c | 6 ++++--
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
index 53378d2dcbec..3c89b9452863 100644
--- a/drivers/gpu/drm/i915/display/intel_crtc.c
+++ b/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -587,7 +587,8 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
 	 */
 	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 = evade.min;
 	crtc->debug.max_vbl = evade.max;
@@ -605,7 +606,8 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
 	return;
 
 irq_disable:
-	local_irq_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_disable();
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_VBLANK_EVADE)
@@ -750,7 +752,8 @@ void intel_pipe_update_end(struct intel_atomic_state *state,
 	if (!state->base.legacy_cursor_update)
 		intel_vrr_send_push(NULL, new_crtc_state);
 
-	local_irq_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_enable();
 
 	if (intel_parent_vgpu_active(display))
 		goto out;
diff --git a/drivers/gpu/drm/i915/display/intel_cursor.c b/drivers/gpu/drm/i915/display/intel_cursor.c
index 2c5d917fbd7e..3477b2cebbe3 100644
--- a/drivers/gpu/drm/i915/display/intel_cursor.c
+++ b/drivers/gpu/drm/i915/display/intel_cursor.c
@@ -919,13 +919,15 @@ intel_legacy_cursor_update(struct drm_plane *_plane,
 		 */
 		intel_psr_wait_for_idle_locked(crtc_state);
 
-		local_irq_disable();
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_disable();
 
 		intel_vblank_evade(&evade);
 
 		drm_crtc_vblank_put(&crtc->base);
 	} else {
-		local_irq_disable();
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+			local_irq_disable();
 	}
 
 	if (new_plane_state->uapi.visible) {
@@ -935,7 +937,8 @@ intel_legacy_cursor_update(struct drm_plane *_plane,
 		intel_plane_disable_arm(NULL, plane, crtc_state);
 	}
 
-	local_irq_enable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_enable();
 
 	intel_psr_unlock(crtc_state);
 
diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index e92fff813505..a540615ba431 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -788,11 +788,13 @@ int intel_vblank_evade(struct intel_vblank_evade_ctx *evade)
 			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);
-- 
2.43.0