[PATCH] drm/i915/guc: Fix a bug in GuC status check

[PATCH] drm/i915/guc: Fix a bug in GuC status check

[yu.dai]

From: Alex Dai <yu.dai@intel.com>

Bit 16 of GuC status indicates resuming from RC6. The LAPIC_DONE
status is a reliable readiness flag only when resuming from RC6.
This fix a racing issue that allocation of doorbell fails whilst
GuC init is not finished.

v2: Split the status check into two parts for better reading and
understanding the code.

Signed-off-by: Alex Dai <yu.dai@intel.com>
---
 drivers/gpu/drm/i915/i915_guc_reg.h     |  1 +
 drivers/gpu/drm/i915/intel_guc_loader.c | 11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_reg.h b/drivers/gpu/drm/i915/i915_guc_reg.h
index 9d79a6b..b355661 100644
--- a/drivers/gpu/drm/i915/i915_guc_reg.h
+++ b/drivers/gpu/drm/i915/i915_guc_reg.h
@@ -37,6 +37,7 @@
 #define   GS_UKERNEL_READY		  (0xF0 << GS_UKERNEL_SHIFT)
 #define   GS_MIA_SHIFT			16
 #define   GS_MIA_MASK			  (0x07 << GS_MIA_SHIFT)
+#define   GS_MIA_CORE_STATE		  (1 << GS_MIA_SHIFT)
 
 #define SOFT_SCRATCH(n)			(0xc180 + ((n) * 4))
 
diff --git a/drivers/gpu/drm/i915/intel_guc_loader.c b/drivers/gpu/drm/i915/intel_guc_loader.c
index e0601cc..98d3ce7 100644
--- a/drivers/gpu/drm/i915/intel_guc_loader.c
+++ b/drivers/gpu/drm/i915/intel_guc_loader.c
@@ -209,9 +209,16 @@ static inline bool guc_ucode_response(struct drm_i915_private *dev_priv,
 				      u32 *status)
 {
 	u32 val = I915_READ(GUC_STATUS);
+	u32 uk_val = val & GS_UKERNEL_MASK;
 	*status = val;
-	return ((val & GS_UKERNEL_MASK) == GS_UKERNEL_READY ||
-		(val & GS_UKERNEL_MASK) == GS_UKERNEL_LAPIC_DONE);
+
+	/* If resuming from RC6, look for LAPIC_DONE */
+	if (val & GS_MIA_CORE_STATE)
+		if (uk_val == GS_UKERNEL_LAPIC_DONE)
+			return true;
+
+	/* Otherwise just check whether the uKernel is READY */
+	return uk_val == GS_UKERNEL_READY;
 }
 
 /*
-- 
1.9.1

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