drm/xe/oa: Assign hwe for OAM_SAG

Because OAM_SAG doesn't have an attached hwe, assign another hwe belonging
to the same gt (and different OAM unit) to OAM_SAG. A hwe is needed for
batch submissions to program OA HW.

v2: Assign an engine with a valid OA unit for OAM_SAG (Umesh)

Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://lore.kernel.org/r/20250606192618.4133817-5-ashutosh.dixit@intel.com

Author: ashutoshx

drivers/gpu/drm/xe/xe_oa.c

@@ -1923,37 +1923,48 @@ u16 xe_oa_unit_id(struct xe_hw_engine *hwe)
 		hwe->oa_unit->oa_unit_id : U16_MAX;
 }
 
+/* A hwe must be assigned to stream/oa_unit for batch submissions */
 static int xe_oa_assign_hwe(struct xe_oa *oa, struct xe_oa_open_param *param)
 {
-	struct xe_gt *gt;
-	int i, ret = 0;
+	struct xe_hw_engine *hwe;
+	enum xe_hw_engine_id id;
+	int ret = 0;
+
+	/* If not provided, OA unit defaults to OA unit 0 as per uapi */
+	if (!param->oa_unit)
+		param->oa_unit = &xe_device_get_gt(oa->xe, 0)->oa.oa_unit[0];
 
+	/* When we have an exec_q, get hwe from the exec_q */
 	if (param->exec_q) {
-		/* When we have an exec_q, get hwe from the exec_q */
 		param->hwe = xe_gt_hw_engine(param->exec_q->gt, param->exec_q->class,
 					     param->engine_instance, true);
-	} else {
-		struct xe_hw_engine *hwe;
-		enum xe_hw_engine_id id;
-
-		/* Else just get the first hwe attached to the oa unit */
-		for_each_gt(gt, oa->xe, i) {
-			for_each_hw_engine(hwe, gt, id) {
-				if (hwe->oa_unit == param->oa_unit) {
-					param->hwe = hwe;
-					goto out;
-				}
-			}
-		}
+		if (!param->hwe || param->hwe->oa_unit != param->oa_unit)
+			goto err;
+		goto out;
 	}
-out:
-	if (!param->hwe || param->hwe->oa_unit != param->oa_unit) {
-		drm_dbg(&oa->xe->drm, "Unable to find hwe (%d, %d) for OA unit ID %d\n",
-			param->exec_q ? param->exec_q->class : -1,
-			param->engine_instance, param->oa_unit->oa_unit_id);
-		ret = -EINVAL;
+
+	/* Else just get the first hwe attached to the oa unit */
+	for_each_hw_engine(hwe, param->oa_unit->gt, id) {
+		if (hwe->oa_unit == param->oa_unit) {
+			param->hwe = hwe;
+			goto out;
+		}
 	}
 
+	/* If we still didn't find a hwe, just get one with a valid oa_unit from the same gt */
+	for_each_hw_engine(hwe, param->oa_unit->gt, id) {
+		if (!hwe->oa_unit)
+			continue;
+
+		param->hwe = hwe;
+		goto out;
+	}
+err:
+	drm_dbg(&oa->xe->drm, "Unable to find hwe (%d, %d) for OA unit ID %d\n",
+		param->exec_q ? param->exec_q->class : -1,
+		param->engine_instance, param->oa_unit->oa_unit_id);
+	ret = -EINVAL;
+out:
 	return ret;
 }
 
@@ -2578,6 +2589,8 @@ static void __xe_oa_init_oa_units(struct xe_gt *gt)
 				DRM_XE_OA_UNIT_TYPE_OAM_SAG : DRM_XE_OA_UNIT_TYPE_OAM;
 		}
 
+		u->gt = gt;
+
 		xe_mmio_write32(&gt->mmio, u->regs.oa_ctrl, 0);
 
 		/* Ensure MMIO trigger remains disabled till there is a stream */

drivers/gpu/drm/xe/xe_oa_types.h

@@ -95,6 +95,9 @@ struct xe_oa_unit {
 	/** @oa_unit_id: identifier for the OA unit */
 	u16 oa_unit_id;
 
+	/** @gt: gt associated with the OA unit */
+	struct xe_gt *gt;
+
 	/** @type: Type of OA unit - OAM, OAG etc. */
 	enum drm_xe_oa_unit_type type;