Re: [Intel-gfx] [PATCH v7 1/4] drm/i915: Introduce intel_gt_mcr_lock_sanitize()

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On 28.09.2023 15:00, Nirmoy Das wrote:
Implement intel_gt_mcr_lock_sanitize() to provide a mechanism
for cleaning the steer semaphore when absolutely necessary.

v2: remove unnecessary lock(Andi, Matt)
     improve the kernel doc(Matt)
     s/intel_gt_mcr_lock_clear/intel_gt_mcr_lock_sanitize

Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 22 ++++++++++++++++++++++
  drivers/gpu/drm/i915/gt/intel_gt_mcr.h |  1 +
  2 files changed, 23 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..326c2ed1d99b 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
@@ -419,6 +419,28 @@ 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_sanitize - Sanitize MCR steering lock
+ * @gt: GT structure
+ *
+ * This will be used to sanitize the initial status of the hardware lock
+ * during driver load and resume since there won't be any concurrent access
+ * from other agents at those times, but it's possible that boot firmware
+ * may have left the lock in a bad state.
+ *
+ */
+void intel_gt_mcr_lock_sanitize(struct intel_gt *gt)
+{
+	/*
+	 * This gets called at load/resume time, so we shouldn't be
+	 * racing with other driver threads grabbing the mcr lock.
+	 */
+	lockdep_assert_not_held(&gt->mcr_lock);
+
+	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
+		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);

I wonder if it wouldn't be useful to check and report if it is locked before unconditional release, no strong feelings.

Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>

Regards
Andrzej


+}
+
  /**
   * 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..01ac565a56a4 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_sanitize(struct intel_gt *gt);
u32 intel_gt_mcr_read(struct intel_gt *gt,
  		      i915_mcr_reg_t reg,




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