1 files changed, 107 insertions, 0 deletions
diff --git a/debian/patches-rt/0001-drm-i915-Use-preempt_disable-enable_rt-where-recomme.patch b/debian/patches-rt/0001-drm-i915-Use-preempt_disable-enable_rt-where-recomme.patch
new file mode 100644
index 0000000000..7c4ce85fa4
--- /dev/null
+++ b/debian/patches-rt/0001-drm-i915-Use-preempt_disable-enable_rt-where-recomme.patch
@@ -0,0 +1,107 @@
+From: Mike Galbraith <umgwanakikbuti@gmail.com>
+Date: Sat, 27 Feb 2016 08:09:11 +0100
+Subject: [PATCH 1/8] drm/i915: Use preempt_disable/enable_rt() where
+ recommended
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.10/older/patches-6.10.2-rt14.tar.xz
+
+Mario Kleiner suggest in commit
+  ad3543ede630f ("drm/intel: Push get_scanout_position() timestamping into kms driver.")
+
+a spots where preemption should be disabled on PREEMPT_RT. The
+difference is that on PREEMPT_RT the intel_uncore::lock disables neither
+preemption nor interrupts and so region remains preemptible.
+
+The area covers only register reads and writes. The part that worries me
+is:
+- __intel_get_crtc_scanline() the worst case is 100us if no match is
+  found.
+
+- intel_crtc_scanlines_since_frame_timestamp() not sure how long this
+  may take in the worst case.
+
+It was in the RT queue for a while and nobody complained.
+Disable preemption on PREEPMPT_RT during timestamping.
+
+[bigeasy: patch description.]
+
+Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
+Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ drivers/gpu/drm/i915/display/intel_vblank.c |   38 ++++++++++++++++++++--------
+ 1 file changed, 28 insertions(+), 10 deletions(-)
+
+--- a/drivers/gpu/drm/i915/display/intel_vblank.c
++++ b/drivers/gpu/drm/i915/display/intel_vblank.c
+@@ -276,6 +276,26 @@ int intel_crtc_scanline_to_hw(struct int
+  * all register accesses to the same cacheline to be serialized,
+  * otherwise they may hang.
+  */
++static void intel_vblank_section_enter_irqsave(struct drm_i915_private *i915, unsigned long *flags)
++	__acquires(i915->uncore.lock)
++{
++#ifdef I915
++	spin_lock_irqsave(&i915->uncore.lock, *flags);
++#else
++	*flags = 0;
++#endif
++}
++
++static void intel_vblank_section_exit_irqrestore(struct drm_i915_private *i915, unsigned long flags)
++	__releases(i915->uncore.lock)
++{
++#ifdef I915
++	spin_unlock_irqrestore(&i915->uncore.lock, flags);
++#else
++	if (flags)
++		return;
++#endif
++}
+ static void intel_vblank_section_enter(struct drm_i915_private *i915)
+ 	__acquires(i915->uncore.lock)
+ {
+@@ -333,10 +353,10 @@ static bool i915_get_crtc_scanoutpos(str
+ 	 * timing critical raw register reads, potentially with
+ 	 * preemption disabled, so the following code must not block.
+ 	 */
+-	local_irq_save(irqflags);
+-	intel_vblank_section_enter(dev_priv);
++	intel_vblank_section_enter_irqsave(dev_priv, &irqflags);
+ 
+-	/* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
++	if (IS_ENABLED(CONFIG_PREEMPT_RT))
++		preempt_disable();
+ 
+ 	/* Get optional system timestamp before query. */
+ 	if (stime)
+@@ -400,10 +420,10 @@ static bool i915_get_crtc_scanoutpos(str
+ 	if (etime)
+ 		*etime = ktime_get();
+ 
+-	/* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */
++	if (IS_ENABLED(CONFIG_PREEMPT_RT))
++		preempt_enable();
+ 
+-	intel_vblank_section_exit(dev_priv);
+-	local_irq_restore(irqflags);
++	intel_vblank_section_exit_irqrestore(dev_priv, irqflags);
+ 
+ 	/*
+ 	 * While in vblank, position will be negative
+@@ -441,13 +461,11 @@ int intel_get_crtc_scanline(struct intel
+ 	unsigned long irqflags;
+ 	int position;
+ 
+-	local_irq_save(irqflags);
+-	intel_vblank_section_enter(dev_priv);
++	intel_vblank_section_enter_irqsave(dev_priv, &irqflags);
+ 
+ 	position = __intel_get_crtc_scanline(crtc);
+ 
+-	intel_vblank_section_exit(dev_priv);
+-	local_irq_restore(irqflags);
++	intel_vblank_section_exit_irqrestore(dev_priv, irqflags);
+ 
+ 	return position;
+ }