From: Mike Galbraith <umgwanakikb...@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...@gmail.com>
Signed-off-by: Mike Galbraith <umgwanakikb...@gmail.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
drivers/gpu/drm/i915/display/intel_vblank.c | 43 ++++++++++++++++-----
1 file changed, 33 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c
b/drivers/gpu/drm/i915/display/intel_vblank.c
index 139fa5deba805..539573113375b 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -312,6 +312,20 @@ static void intel_vblank_section_exit(struct intel_display
*display)
struct drm_i915_private *i915 = to_i915(display->drm);
spin_unlock(&i915->uncore.lock);
}
+
+static void intel_vblank_section_enter_irqf(struct intel_display *display,
unsigned long *flags)
+ __acquires(i915->uncore.lock)
+{
+ struct drm_i915_private *i915 = to_i915(display->drm);
+ spin_lock_irqsave(&i915->uncore.lock, *flags);
+}
+
+static void intel_vblank_section_exit_irqf(struct intel_display *display,
unsigned long flags)
+ __releases(i915->uncore.lock)
+{
+ struct drm_i915_private *i915 = to_i915(display->drm);
+ spin_unlock_irqrestore(&i915->uncore.lock, flags);
+}
#else
static void intel_vblank_section_enter(struct intel_display *display)
{
@@ -320,6 +334,17 @@ static void intel_vblank_section_enter(struct
intel_display *display)
static void intel_vblank_section_exit(struct intel_display *display)
{
}
+
+static void intel_vblank_section_enter_irqf(struct intel_display *display,
unsigned long *flags)
+{
+ *flags = 0;
+}
+
+static void intel_vblank_section_exit_irqf(struct intel_display *display,
unsigned long flags)
+{
+ if (flags)
+ return;
+}
#endif
static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
@@ -356,10 +381,10 @@ static bool i915_get_crtc_scanoutpos(struct drm_crtc
*_crtc,
* timing critical raw register reads, potentially with
* preemption disabled, so the following code must not block.
*/
- local_irq_save(irqflags);
- intel_vblank_section_enter(display);
+ intel_vblank_section_enter_irqf(display, &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)
@@ -423,10 +448,10 @@ 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();
- intel_vblank_section_exit(display);
- local_irq_restore(irqflags);
+ intel_vblank_section_exit_irqf(display, irqflags);
/*
* While in vblank, position will be negative
@@ -464,13 +489,11 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc)
unsigned long irqflags;
int position;
- local_irq_save(irqflags);
- intel_vblank_section_enter(display);
+ intel_vblank_section_enter_irqf(display, &irqflags);
position = __intel_get_crtc_scanline(crtc);
- intel_vblank_section_exit(display);
- local_irq_restore(irqflags);
+ intel_vblank_section_exit_irqf(display, irqflags);
return position;
}
--
2.50.0
