libata-link: introduce ata_link

Introduce ata_link.  It abstracts PHY and sits between ata_port and
ata_device.  This new level of abstraction is necessary to support
SATA Port Multiplier, which basically adds a bunch of links (PHYs) to
a ATA host port.  Fields related to command execution, spd_limit and
EH are per-link and thus moved to ata_link.

This patch only defines the host link.  Multiple link handling will be
added later.  Also, a lot of ap->link derefences are added but many of
them will be removed as each part is converted to deal directly with
ata_link instead of ata_port.

This patch introduces no behavior change.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/sata_promise.c b/drivers/ata/sata_promise.c
index 25698cf..620d067 100644
--- a/drivers/ata/sata_promise.c
+++ b/drivers/ata/sata_promise.c
@@ -626,7 +626,7 @@
 static void pdc_error_intr(struct ata_port *ap, struct ata_queued_cmd *qc,
 			   u32 port_status, u32 err_mask)
 {
-	struct ata_eh_info *ehi = &ap->eh_info;
+	struct ata_eh_info *ehi = &ap->link.eh_info;
 	unsigned int ac_err_mask = 0;
 
 	ata_ehi_clear_desc(ehi);
@@ -773,7 +773,7 @@
 		tmp = hotplug_status & (0x11 << ata_no);
 		if (tmp && ap &&
 		    !(ap->flags & ATA_FLAG_DISABLED)) {
-			struct ata_eh_info *ehi = &ap->eh_info;
+			struct ata_eh_info *ehi = &ap->link.eh_info;
 			ata_ehi_clear_desc(ehi);
 			ata_ehi_hotplugged(ehi);
 			ata_ehi_push_desc(ehi, "hotplug_status %#x", tmp);
@@ -788,7 +788,7 @@
 		    !(ap->flags & ATA_FLAG_DISABLED)) {
 			struct ata_queued_cmd *qc;
 
-			qc = ata_qc_from_tag(ap, ap->active_tag);
+			qc = ata_qc_from_tag(ap, ap->link.active_tag);
 			if (qc && (!(qc->tf.flags & ATA_TFLAG_POLLING)))
 				handled += pdc_host_intr(ap, qc);
 		}