[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

 	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
  *
 		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

 	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 */