drm/i915: Don't check for atomic context on PREEMPT_RT

The !in_atomic() check in _wait_for_atomic() triggers on PREEMPT_RT
because the uncore::lock is a spinlock_t and does not disable
preemption or interrupts.

Changing the uncore:lock to a raw_spinlock_t doubles the worst case
latency on an otherwise idle testbox during testing.

Ignore _WAIT_FOR_ATOMIC_CHECK() on PREEMPT_RT.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://lore.kernel.org/all/20211006164628.s2mtsdd2jdbfyf7g@linutronix.de/
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250714153954.629393-4-bigeasy@linutronix.de
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>

diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index f7fb40cfdb7058618cbb260f90f34245a037f796..9cb40c2c4b124ca99654aebab43a05517478bdc2 100644 (file)
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -267,8 +267,13 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
                                                   (Wmax))
 #define wait_for(COND, MS)             _wait_for((COND), (MS) * 1000, 10, 1000)
 
-/* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
-#if IS_ENABLED(CONFIG_DRM_I915_DEBUG) && IS_ENABLED(CONFIG_PREEMPT_COUNT)
+/*
+ * If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false.
+ * On PREEMPT_RT the context isn't becoming atomic because it is used in an
+ * interrupt handler or because a spinlock_t is acquired. This leads to
+ * warnings which don't occur otherwise and therefore the check is disabled.
+ */
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG) && IS_ENABLED(CONFIG_PREEMPT_COUNT) && !defined(CONFIG_PREEMPT_RT)
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
 #else
 # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)