[PATCH] libata: implement ata_port_max_devices()

Implement ata_port_max_devices().  This function returns the number of
possible devices on a port.  This will be used by new PM
implementation.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

include/linux/libata.h

@@ -888,6 +888,9 @@ static inline unsigned int ata_tag_internal(unsigned int tag)
 	return tag == ATA_MAX_QUEUE - 1;
 }
 
+/*
+ * device helpers
+ */
 static inline unsigned int ata_class_enabled(unsigned int class)
 {
 	return class == ATA_DEV_ATA || class == ATA_DEV_ATAPI;
@@ -918,6 +921,17 @@ static inline unsigned int ata_dev_absent(const struct ata_device *dev)
 	return ata_class_absent(dev->class);
 }
 
+/*
+ * port helpers
+ */
+static inline int ata_port_max_devices(const struct ata_port *ap)
+{
+	if (ap->flags & ATA_FLAG_SLAVE_POSS)
+		return 2;
+	return 1;
+}
+
+
 static inline u8 ata_chk_status(struct ata_port *ap)
 {
 	return ap->ops->check_status(ap);