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drm/i915: Use preempt_disable/enable_rt() where recommended

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BugLink: https://bugs.launchpad.net/bugs/2060704

Mario Kleiner suggest in commit
  ad3543ede6 ("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>
Signed-off-by: Kevin Becker <kevin.becker@canonical.com>
This commit is contained in:
Mike Galbraith
2016-02-27 08:09:11 +01:00
committed by Kevin Becker
parent 26331faec8
commit 8ef07efdde
1 changed files with 28 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files
drivers/gpu/drm/i915/display/intel_vblank.c
+28 -10
View File
@@ -275,6 +275,26 @@ int intel_crtc_scanline_to_hw(struct intel_crtc *crtc, int scanline)
* 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)
{
@@ -332,10 +352,10 @@ 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(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)
@@ -399,10 +419,10 @@ 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(dev_priv);
local_irq_restore(irqflags);
intel_vblank_section_exit_irqrestore(dev_priv, irqflags);
/*
* While in vblank, position will be negative
@@ -440,13 +460,11 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc)
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;
}