drm/xe: hold mem_access.ref for CT fast-path

Just checking xe_device_mem_access_ongoing() is not enough, we also need
to hold the reference otherwise the ref can transition from 1 -> 0 as we
enter g2h_read(), leading to warnings. While we can't do a full rpm sync
in the IRQ, we can keep the device awake if the ref is non-zero.
Introduce a new helper for this and set it to work in for the CT
fast-path.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_device.c

@@ -364,6 +364,11 @@ u32 xe_device_ccs_bytes(struct xe_device *xe, u64 size)
 		DIV_ROUND_UP(size, NUM_BYTES_PER_CCS_BYTE) : 0;
 }
 
+bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe)
+{
+	return atomic_inc_not_zero(&xe->mem_access.ref);
+}
+
 void xe_device_mem_access_get(struct xe_device *xe)
 {
 	bool resumed = xe_pm_runtime_resume_if_suspended(xe);

drivers/gpu/drm/xe/xe_device.h

@@ -138,6 +138,7 @@ static inline struct xe_force_wake * gt_to_fw(struct xe_gt *gt)
 }
 
 void xe_device_mem_access_get(struct xe_device *xe);
+bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe);
 void xe_device_mem_access_put(struct xe_device *xe);
 
 static inline bool xe_device_mem_access_ongoing(struct xe_device *xe)

drivers/gpu/drm/xe/xe_guc_ct.c

@@ -1044,7 +1044,8 @@ void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
 	struct xe_device *xe = ct_to_xe(ct);
 	int len;
 
-	if (!xe_device_in_fault_mode(xe) || !xe_device_mem_access_ongoing(xe))
+	if (!xe_device_in_fault_mode(xe) ||
+	    !xe_device_mem_access_get_if_ongoing(xe))
 		return;
 
 	spin_lock(&ct->fast_lock);
@@ -1054,6 +1055,8 @@ void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
 			g2h_fast_path(ct, ct->fast_msg, len);
 	} while (len > 0);
 	spin_unlock(&ct->fast_lock);
+
+	xe_device_mem_access_put(xe);
 }
 
 /* Returns less than zero on error, 0 on done, 1 on more available */