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>

drivers/ata/sata_sil.c

@@ -312,7 +312,7 @@ static int sil_set_mode (struct ata_port *ap, struct ata_device **r_failed)
 		return rc;
 
 	for (i = 0; i < 2; i++) {
-		dev = &ap->device[i];
+		dev = &ap->link.device[i];
 		if (!ata_dev_enabled(dev))
 			dev_mode[i] = 0;	/* PIO0/1/2 */
 		else if (dev->flags & ATA_DFLAG_PIO)
@@ -374,8 +374,8 @@ static int sil_scr_write(struct ata_port *ap, unsigned int sc_reg, u32 val)
 
 static void sil_host_intr(struct ata_port *ap, u32 bmdma2)
 {
-	struct ata_eh_info *ehi = &ap->eh_info;
-	struct ata_queued_cmd *qc = ata_qc_from_tag(ap, ap->active_tag);
+	struct ata_eh_info *ehi = &ap->link.eh_info;
+	struct ata_queued_cmd *qc = ata_qc_from_tag(ap, ap->link.active_tag);
 	u8 status;
 
 	if (unlikely(bmdma2 & SIL_DMA_SATA_IRQ)) {
@@ -394,8 +394,8 @@ static void sil_host_intr(struct ata_port *ap, u32 bmdma2)
 		 * repeat probing needlessly.
 		 */
 		if (!(ap->pflags & ATA_PFLAG_FROZEN)) {
-			ata_ehi_hotplugged(&ap->eh_info);
-			ap->eh_info.serror |= serror;
+			ata_ehi_hotplugged(&ap->link.eh_info);
+			ap->link.eh_info.serror |= serror;
 		}
 
 		goto freeze;
@@ -562,8 +562,8 @@ static void sil_thaw(struct ata_port *ap)
  */
 static void sil_dev_config(struct ata_device *dev)
 {
-	struct ata_port *ap = dev->ap;
-	int print_info = ap->eh_context.i.flags & ATA_EHI_PRINTINFO;
+	struct ata_port *ap = dev->link->ap;
+	int print_info = ap->link.eh_context.i.flags & ATA_EHI_PRINTINFO;
 	unsigned int n, quirks = 0;
 	unsigned char model_num[ATA_ID_PROD_LEN + 1];