[RFC PATCH 37/97] drm/i915/guc: Add stall timer to non blocking CTB send function

[Matthew Brost <matthew.brost@xxxxxxxxx>]

Implement a stall timer which fails H2G CTBs once a period of time
with no forward progress is reached to prevent deadlock.

Also update to ct_write to return -EDEADLK rather than -EPIPE on a
corrupted descriptor.

Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 48 +++++++++++++++++++++--
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
index af7314d45a78..4eab319d61be 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
@@ -69,6 +69,8 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
 #define CTB_H2G_BUFFER_SIZE	(SZ_4K)
 #define CTB_G2H_BUFFER_SIZE	(SZ_4K)
 
+#define MAX_US_STALL_CTB	1000000
+
 struct ct_request {
 	struct list_head link;
 	u32 fence;
@@ -315,6 +317,7 @@ int intel_guc_ct_enable(struct intel_guc_ct *ct)
 
 	ct->requests.last_fence = 1;
 	ct->enabled = true;
+	ct->stall_time = KTIME_MAX;
 
 	return 0;
 
@@ -378,7 +381,7 @@ static int ct_write(struct intel_guc_ct *ct,
 	unsigned int i;
 
 	if (unlikely(ctb->broken))
-		return -EPIPE;
+		return -EDEADLK;
 
 	if (unlikely(desc->status))
 		goto corrupted;
@@ -449,7 +452,7 @@ static int ct_write(struct intel_guc_ct *ct,
 	CT_ERROR(ct, "Corrupted descriptor head=%u tail=%u status=%#x\n",
 		 desc->head, desc->tail, desc->status);
 	ctb->broken = true;
-	return -EPIPE;
+	return -EDEADLK;
 }
 
 /**
@@ -494,6 +497,17 @@ static int wait_for_ct_request_update(struct ct_request *req, u32 *status)
 	return err;
 }
 
+static inline bool ct_deadlocked(struct intel_guc_ct *ct)
+{
+	bool ret = ktime_us_delta(ktime_get(), ct->stall_time) >
+		MAX_US_STALL_CTB;
+
+	if (unlikely(ret))
+		CT_ERROR(ct, "CT deadlocked\n");
+
+	return ret;
+}
+
 static inline bool ctb_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
 {
 	struct guc_ct_buffer_desc *desc = ctb->desc;
@@ -505,6 +519,26 @@ static inline bool ctb_has_room(struct intel_guc_ct_buffer *ctb, u32 len_dw)
 	return space >= len_dw;
 }
 
+static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
+{
+	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
+
+	lockdep_assert_held(&ct->ctbs.send.lock);
+
+	if (unlikely(!ctb_has_room(ctb, len_dw))) {
+		if (ct->stall_time == KTIME_MAX)
+			ct->stall_time = ktime_get();
+
+		if (unlikely(ct_deadlocked(ct)))
+			return -EDEADLK;
+		else
+			return -EBUSY;
+	}
+
+	ct->stall_time = KTIME_MAX;
+	return 0;
+}
+
 static int ct_send_nb(struct intel_guc_ct *ct,
 		      const u32 *action,
 		      u32 len,
@@ -517,7 +551,7 @@ static int ct_send_nb(struct intel_guc_ct *ct,
 
 	spin_lock_irqsave(&ctb->lock, spin_flags);
 
-	ret = ctb_has_room(ctb, len + 1);
+	ret = has_room_nb(ct, len + 1);
 	if (unlikely(ret))
 		goto out;
 
@@ -561,11 +595,19 @@ static int ct_send(struct intel_guc_ct *ct,
 retry:
 	spin_lock_irqsave(&ct->ctbs.send.lock, flags);
 	if (unlikely(!ctb_has_room(ctb, len + 1))) {
+		if (ct->stall_time == KTIME_MAX)
+			ct->stall_time = ktime_get();
 		spin_unlock_irqrestore(&ct->ctbs.send.lock, flags);
+
+		if (unlikely(ct_deadlocked(ct)))
+			return -EDEADLK;
+
 		cond_resched();
 		goto retry;
 	}
 
+	ct->stall_time = KTIME_MAX;
+
 	fence = ct_get_next_fence(ct);
 	request.fence = fence;
 	request.status = 0;
-- 
2.28.0