[PATCH v3 2/2] drm/xe/guc: READ/WRITE_ONCE ct->state

[Jonathan Cavitt <jonathan.cavitt@intel.com>]

Use READ_ONCE and WRITE_ONCE when operating on ct->state
to prevent the compiler form ignoring important modifications
to its value.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
---
 drivers/gpu/drm/xe/xe_guc_ct.c | 7 ++++++-
 drivers/gpu/drm/xe/xe_guc_ct.h | 6 ++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index f2148a8bf208..dfbf76037b04 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -529,7 +529,12 @@ static void guc_ct_change_state(struct xe_guc_ct *ct,
 	if (ct->g2h_outstanding)
 		xe_pm_runtime_put(ct_to_xe(ct));
 	ct->g2h_outstanding = 0;
-	ct->state = state;
+
+	/*
+	 * WRITE_ONCE pairs with READ_ONCEs in xe_guc_ct_initialized and
+	 * xe_guc_ct_enabled.
+	 */
+	WRITE_ONCE(ct->state, state);
 
 	xe_gt_dbg(gt, "GuC CT communication channel %s\n",
 		  state == XE_GUC_CT_STATE_STOPPED ? "stopped" :
diff --git a/drivers/gpu/drm/xe/xe_guc_ct.h b/drivers/gpu/drm/xe/xe_guc_ct.h
index 5599939f8fe1..767365a33dee 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.h
+++ b/drivers/gpu/drm/xe/xe_guc_ct.h
@@ -30,12 +30,14 @@ void xe_guc_ct_print(struct xe_guc_ct *ct, struct drm_printer *p, bool want_ctb)
 
 static inline bool xe_guc_ct_initialized(struct xe_guc_ct *ct)
 {
-	return ct->state != XE_GUC_CT_STATE_NOT_INITIALIZED;
+	/* READ_ONCE pairs with WRITE_ONCE in guc_ct_change_state. */
+	return READ_ONCE(ct->state) != XE_GUC_CT_STATE_NOT_INITIALIZED;
 }
 
 static inline bool xe_guc_ct_enabled(struct xe_guc_ct *ct)
 {
-	return ct->state == XE_GUC_CT_STATE_ENABLED;
+	/* READ_ONCE pairs with WRITE_ONCE in guc_ct_change_state. */
+	return READ_ONCE(ct->state) == XE_GUC_CT_STATE_ENABLED;
 }
 
 static inline void xe_guc_ct_irq_handler(struct xe_guc_ct *ct)
-- 
2.43.0