[PATCH v3 22/36] drm/xe/vf: Use GUC_HXG_TYPE_EVENT for GuC context register

[Matthew Brost <matthew.brost@intel.com>]

The only case where the GuC submission backend cannot reason 100%
correctly is when a GuC context is registered during VF post-migration
recovery. In this scenario, it's possible that the GuC context register
H2G is processed, but the immediately following schedule-enable H2G gets
lost.

A double register is harmless when using `GUC_HXG_TYPE_EVENT`, as GuC
simply drops the duplicate H2G. To keep things simple, use
`GUC_HXG_TYPE_EVENT` for all context registrations on VFs.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_guc_ct.c | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index d0fde371fae3..d84de8544532 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -736,6 +736,26 @@ static u16 next_ct_seqno(struct xe_guc_ct *ct, bool is_g2h_fence)
 	return seqno;
 }
 
+#define MAKE_ACTION(type, __action)				\
+({								\
+	FIELD_PREP(GUC_HXG_MSG_0_TYPE, type) |			\
+	FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |			\
+		   GUC_HXG_EVENT_MSG_0_DATA0, __action);	\
+})
+
+static bool vf_action_can_safely_fail(struct xe_device *xe, u32 action)
+{
+	/*
+	 * If we are VF resuming, we can't exactly track if a context
+	 * registration has been completed in the GuC state machine, it is
+	 * harmless to resend as it will just fail silently if
+	 * GUC_HXG_TYPE_EVENT is used.
+	 */
+	return IS_SRIOV_VF(xe) &&
+		(action == XE_GUC_ACTION_REGISTER_CONTEXT_MULTI_LRC ||
+		 action == XE_GUC_ACTION_REGISTER_CONTEXT);
+}
+
 #define H2G_CT_HEADERS (GUC_CTB_HDR_LEN + 1) /* one DW CTB header and one DW HxG header */
 
 static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
@@ -807,18 +827,14 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
 		FIELD_PREP(GUC_CTB_MSG_0_NUM_DWORDS, len) |
 		FIELD_PREP(GUC_CTB_MSG_0_FENCE, ct_fence_value);
 	if (want_response) {
-		cmd[1] =
-			FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_REQUEST) |
-			FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
-				   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
+		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_REQUEST, action[0]);
+	} else if (vf_action_can_safely_fail(xe, action[0])) {
+		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_EVENT, action[0]);
 	} else {
 		fast_req_track(ct, ct_fence_value,
 			       FIELD_GET(GUC_HXG_EVENT_MSG_0_ACTION, action[0]));
 
-		cmd[1] =
-			FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_FAST_REQUEST) |
-			FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
-				   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
+		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_FAST_REQUEST, action[0]);
 	}
 
 	/* H2G header in cmd[1] replaces action[0] so: */
-- 
2.34.1