From: Mike Galbraith umgwanakikbuti@gmail.com
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/i915_irq.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index 9bc4f4a8e12ec..547347241a47c 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -886,7 +886,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, */ spin_lock_irqsave(&dev_priv->uncore.lock, 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) @@ -950,7 +951,8 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc, if (etime) *etime = ktime_get();
- /* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable();
spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);