[PATCH] drm/i915/gt: Swap the order of mcr lock and spinlock

[Andi Shyti]

Until now we first have taken the mcr steering semaphore in
hardware and then the mcr_lock spinlock in KMD.

But when performing a big amount of MCR lock/unlock, like during
TLB invalidation, the time between MCR steering semaphore lock
and the spinlock is liable to a locking contention in the steer
semaphore register; especially considering that there is a
waiting timeout for the MCR lock.

Swap the order of the locks to ensure proper serialization of the
MCR steering semaphore lock access.

Suggested-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
index 326c2ed1d99b..e33b33f8deb2 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
@@ -371,6 +371,14 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags)
 
 	lockdep_assert_not_held(&gt->uncore->lock);
 
+	/*
+	 * Even on platforms with a hardware lock, we'll continue to grab
+	 * a software spinlock too for lockdep purposes.  If the hardware lock
+	 * was already acquired, there should never be contention on the
+	 * software lock.
+	 */
+	spin_lock_irqsave(&gt->mcr_lock, __flags);
+
 	/*
 	 * Starting with MTL, we need to coordinate not only with other
 	 * driver threads, but also with hardware/firmware agents.  A dedicated
@@ -380,14 +388,6 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags)
 		err = wait_for(intel_uncore_read_fw(gt->uncore,
 						    MTL_STEER_SEMAPHORE) == 0x1, 100);
 
-	/*
-	 * Even on platforms with a hardware lock, we'll continue to grab
-	 * a software spinlock too for lockdep purposes.  If the hardware lock
-	 * was already acquired, there should never be contention on the
-	 * software lock.
-	 */
-	spin_lock_irqsave(&gt->mcr_lock, __flags);
-
 	*flags = __flags;
 
 	/*
@@ -413,10 +413,10 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags)
 void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags)
 	__releases(&gt->mcr_lock)
 {
-	spin_unlock_irqrestore(&gt->mcr_lock, flags);
-
 	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
 		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
+
+	spin_unlock_irqrestore(&gt->mcr_lock, flags);
 }
 
 /**
-- 
2.40.1