[linda] Wait up to 20us for link state to update

Some subnet managers expect the GetResponse from a SetPortInfo MAD to
contain the new link state.  The transition is not immediate, so we
often end up returning the previous link state.  This can cause the SM
to fail to activate the port.

Fix by waiting for up to 20us for the link state transition to take
effect.

src/drivers/infiniband/linda.c

@@ -238,6 +238,32 @@ static void linda_link_state_changed ( struct ib_device *ibdev ) {
 	ib_link_state_changed ( ibdev );
 }
 
+/**
+ * Wait for link state change to take effect
+ *
+ * @v linda		Linda device
+ * @v new_link_state	Expected link state
+ * @ret rc		Return status code
+ */
+static int linda_link_state_check ( struct linda *linda,
+				    unsigned int new_link_state ) {
+	struct QIB_7220_IBCStatus ibcstatus;
+	unsigned int link_state;
+	unsigned int i;
+
+	for ( i = 0 ; i < LINDA_LINK_STATE_MAX_WAIT_US ; i++ ) {
+		linda_readq ( linda, &ibcstatus, QIB_7220_IBCStatus_offset );
+		link_state = BIT_GET ( &ibcstatus, LinkState );
+		if ( link_state == new_link_state )
+			return 0;
+		udelay ( 1 );
+	}
+
+	DBGC ( linda, "Linda %p timed out waiting for link state %s\n",
+	       linda, linda_link_state_text ( link_state ) );
+	return -ETIMEDOUT;
+}
+
 /**
  * Set port information
  *
@@ -260,6 +286,12 @@ static int linda_set_port_info ( struct ib_device *ibdev, union ib_mad *mad ) {
 		linda_readq ( linda, &ibcctrl, QIB_7220_IBCCtrl_offset );
 		BIT_SET ( &ibcctrl, LinkCmd, link_state );
 		linda_writeq ( linda, &ibcctrl, QIB_7220_IBCCtrl_offset );
+
+		/* Wait for link state change to take effect.  Ignore
+		 * errors; the current link state will be returned via
+		 * the GetResponse MAD.
+		 */
+		linda_link_state_check ( linda, link_state );
 	}
 
 	/* Detect and report link state change */

src/drivers/infiniband/linda.h

@@ -270,4 +270,7 @@ enum linda_link_state {
 	LINDA_LINK_STATE_ACT_DEFER = 4,
 };
 
+/** Maximum time to wait for link state changes, in us */
+#define LINDA_LINK_STATE_MAX_WAIT_US 20
+
 #endif /* _LINDA_H */