108 lines
3.5 KiB
Diff
108 lines
3.5 KiB
Diff
|
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/6.11/older/patches-6.11-rt7.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
|
||
|
|
@@ -303,6 +303,26 @@ 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)
|
||
|
|
{
|
||
|
|
@@ -354,10 +374,10 @@ 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)
|
||
|
|
@@ -421,10 +441,10 @@ 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
|
||
|
|
@@ -462,13 +482,11 @@ 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;
|
||
|
|
}
|