[PATCH 1/4] drm/i915: Introduce intel_gt_mcr_lock_reset()

[Nirmoy Das]

Implement intel_gt_mcr_lock_reset() to provide a mechanism
for resetting the steer semaphore when absolutely necessary.

Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 32 ++++++++++++++++++++++++++
 drivers/gpu/drm/i915/gt/intel_gt_mcr.h |  1 +
 2 files changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
index bf4a933de03a..f4c4ae5745ef 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
@@ -419,6 +419,38 @@ void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags)
 		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
 }
 
+/**
+ * intel_gt_mcr_lock_reset - Reset MCR steering lock
+ * @gt: GT structure
+ *
+ * Performs a steer semaphore reset operation. On MTL and beyond, a hardware
+ * lock will also be taken to serialize access not only for the driver,
+ * but also for external hardware and firmware agents.
+ * However, there may be situations where the driver must reset the semaphore
+ * but only when it is absolutely certain that no other agent should own the
+ * lock at that given time.
+ *
+ * Context: Takes gt->mcr_lock.  uncore->lock should *not* be held when this
+ *          function is called, although it may be acquired after this
+ *          function call.
+ */
+void intel_gt_mcr_lock_reset(struct intel_gt *gt)
+{
+	unsigned long __flags;
+
+	lockdep_assert_not_held(&gt->uncore->lock);
+
+	gt_info(gt, "intel_gt_mcr_lock_reset called\n");
+	spin_lock_irqsave(&gt->mcr_lock, __flags);
+
+	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70)) {
+		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
+		dump_stack();
+	}
+
+	spin_unlock_irqrestore(&gt->mcr_lock, __flags);
+}
+
 /**
  * intel_gt_mcr_read - read a specific instance of an MCR register
  * @gt: GT structure
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
index 41684495b7da..485c7711f2e8 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
@@ -11,6 +11,7 @@
 void intel_gt_mcr_init(struct intel_gt *gt);
 void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags);
 void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags);
+void intel_gt_mcr_lock_reset(struct intel_gt *gt);
 
 u32 intel_gt_mcr_read(struct intel_gt *gt,
 		      i915_mcr_reg_t reg,
-- 
2.41.0