ahci: update PCS programming

For intel ones, ahci unconditionally OR'd 0xf to PCS.  This isn't
correct for the following cases.

* ich6/7m's which only implement P0 and P2 (0xf works fine tho)

* ich8/9's which have six ports and needs 0x3f to enable all ports

This patch updates PCS programming such that...

* port_map determined by ahci_save_initial_config() is OR'd instead of 0xf

* PCS is updated only if necessary (there are turned off enable bits)

port_map is determined from PORTS_IMPL PCI register which is
implemented as write or write-once register.  If the register isn't
programmed, ahci automatically generates it from number of ports,
which is good enough for PCS programming.  ICH6/7M are probably the
only ones where non-contiguous enable bits are necessary && PORTS_IMPL
isn't programmed properly but they're proven to work reliably with 0xf
anyway.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/ahci.c

@@ -1036,6 +1036,7 @@ static int ahci_deinit_port(struct ata_port *ap, const char **emsg)
 static int ahci_reset_controller(struct ata_host *host)
 {
 	struct pci_dev *pdev = to_pci_dev(host->dev);
+	struct ahci_host_priv *hpriv = host->private_data;
 	void __iomem *mmio = host->iomap[AHCI_PCI_BAR];
 	u32 tmp;
 
@@ -1078,8 +1079,10 @@ static int ahci_reset_controller(struct ata_host *host)
 
 		/* configure PCS */
 		pci_read_config_word(pdev, 0x92, &tmp16);
-		tmp16 |= 0xf;
-		pci_write_config_word(pdev, 0x92, tmp16);
+		if ((tmp16 & hpriv->port_map) != hpriv->port_map) {
+			tmp16 |= hpriv->port_map;
+			pci_write_config_word(pdev, 0x92, tmp16);
+		}
 	}
 
 	return 0;