libata: implement slave_link

Explanation taken from the comment of ata_slave_link_init().

 In libata, a port contains links and a link contains devices.  There
 is single host link but if a PMP is attached to it, there can be
 multiple fan-out links.  On SATA, there's usually a single device
 connected to a link but PATA and SATA controllers emulating TF based
 interface can have two - master and slave.

 However, there are a few controllers which don't fit into this
 abstraction too well - SATA controllers which emulate TF interface
 with both master and slave devices but also have separate SCR
 register sets for each device.  These controllers need separate links
 for physical link handling (e.g. onlineness, link speed) but should
 be treated like a traditional M/S controller for everything else
 (e.g. command issue, softreset).

 slave_link is libata's way of handling this class of controllers
 without impacting core layer too much.  For anything other than
 physical link handling, the default host link is used for both master
 and slave.  For physical link handling, separate @ap->slave_link is
 used.  All dirty details are implemented inside libata core layer.
 From LLD's POV, the only difference is that prereset, hardreset and
 postreset are called once more for the slave link, so the reset
 sequence looks like the following.

 prereset(M) -> prereset(S) -> hardreset(M) -> hardreset(S) ->
 softreset(M) -> postreset(M) -> postreset(S)

 Note that softreset is called only for the master.  Softreset resets
 both M/S by definition, so SRST on master should handle both (the
 standard method will work just fine).

As slave_link excludes PMP support and only code paths which deal with
the attributes of physical link are affected, all the changes are
localized to libata.h, libata-core.c and libata-eh.c.

 * ata_is_host_link() updated so that slave_link is considered as host
   link too.

 * iterator extended to iterate over the slave_link when using the
   underbarred version.

 * force param handling updated such that devno 16 is mapped to the
   slave link/device.

 * ata_link_on/offline() updated to return the combined result from
   master and slave link.  ata_phys_link_on/offline() are the direct
   versions.

 * EH autopsy and report are performed separately for master slave
   links.  Reset is udpated to implement the above described reset
   sequence.

Except for reset update, most changes are minor, many of them just
modifying dev->link to ata_dev_phys_link(dev) or using phys online
test instead.

After this update, LLDs can take full advantage of per-dev SCR
registers by simply turning on slave link.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/include/linux/libata.h b/include/linux/libata.h
index 0c7e6f3..244ff60 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -690,7 +690,8 @@ struct ata_port {
 	unsigned int		qc_active;
 	int			nr_active_links; /* #links with active qcs */
 
-	struct ata_link		link;	/* host default link */
+	struct ata_link		link;		/* host default link */
+	struct ata_link		*slave_link;	/* see ata_slave_link_init() */
 
 	int			nr_pmp_links;	/* nr of available PMP links */
 	struct ata_link		*pmp_link;	/* array of PMP links */
@@ -897,6 +898,7 @@ extern void ata_port_disable(struct ata_port *);
 extern struct ata_host *ata_host_alloc(struct device *dev, int max_ports);
 extern struct ata_host *ata_host_alloc_pinfo(struct device *dev,
 			const struct ata_port_info * const * ppi, int n_ports);
+extern int ata_slave_link_init(struct ata_port *ap);
 extern int ata_host_start(struct ata_host *host);
 extern int ata_host_register(struct ata_host *host,
 			     struct scsi_host_template *sht);
@@ -1136,7 +1138,7 @@ static inline bool sata_pmp_attached(struct ata_port *ap)
 
 static inline int ata_is_host_link(const struct ata_link *link)
 {
-	return link == &link->ap->link;
+	return link == &link->ap->link || link == link->ap->slave_link;
 }
 #else /* CONFIG_SATA_PMP */
 static inline bool sata_pmp_supported(struct ata_port *ap)
@@ -1169,7 +1171,7 @@ static inline int sata_srst_pmp(struct ata_link *link)
 	printk("%sata%u: "fmt, lv, (ap)->print_id , ##args)
 
 #define ata_link_printk(link, lv, fmt, args...) do { \
-	if (sata_pmp_attached((link)->ap)) \
+	if (sata_pmp_attached((link)->ap) || (link)->ap->slave_link)	\
 		printk("%sata%u.%02u: "fmt, lv, (link)->ap->print_id,	\
 		       (link)->pmp , ##args); \
 	else \