libata-pmp: implement qc_defer for command switching PMP support

Implement sata_pmp_qc_defer_cmd_switch() - standard qc_defer for
command switching PMP support.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -7303,6 +7303,7 @@ EXPORT_SYMBOL_GPL(ata_pci_default_filter);
 EXPORT_SYMBOL_GPL(ata_pci_clear_simplex);
 #endif /* CONFIG_PCI */
 
+EXPORT_SYMBOL_GPL(sata_pmp_qc_defer_cmd_switch);
 EXPORT_SYMBOL_GPL(sata_pmp_read_init_tf);
 EXPORT_SYMBOL_GPL(sata_pmp_read_val);
 EXPORT_SYMBOL_GPL(sata_pmp_write_init_tf);

drivers/ata/libata-pmp.c

@@ -69,6 +69,36 @@ static int sata_pmp_write(struct ata_link *link, int reg, u32 val)
 	return rc;
 }
 
+/**
+ *	sata_pmp_qc_defer_cmd_switch - qc_defer for command switching PMP
+ *	@qc: ATA command in question
+ *
+ *	A host which has command switching PMP support cannot issue
+ *	commands to multiple links simultaneously.
+ *
+ *	LOCKING:
+ *	spin_lock_irqsave(host lock)
+ *
+ *	RETURNS:
+ *	ATA_DEFER_* if deferring is needed, 0 otherwise.
+ */
+int sata_pmp_qc_defer_cmd_switch(struct ata_queued_cmd *qc)
+{
+	struct ata_link *link = qc->dev->link;
+	struct ata_port *ap = link->ap;
+
+	if (ap->excl_link == NULL || ap->excl_link == link) {
+		if (ap->nr_active_links == 0 || ata_link_active(link)) {
+			qc->flags |= ATA_QCFLAG_CLEAR_EXCL;
+			return ata_std_qc_defer(qc);
+		}
+
+		ap->excl_link = link;
+	}
+
+	return ATA_DEFER_PORT;
+}
+
 /**
  *	sata_pmp_read_init_tf - initialize TF for PMP read
  *	@tf: taskfile to initialize

include/linux/libata.h

@@ -947,6 +947,7 @@ extern unsigned long ata_pci_default_filter(struct ata_device *, unsigned long);
 /*
  * PMP
  */
+extern int sata_pmp_qc_defer_cmd_switch(struct ata_queued_cmd *qc);
 extern void sata_pmp_read_init_tf(struct ata_taskfile *tf,
 				  struct ata_device *dev, int pmp, int reg);
 extern u32 sata_pmp_read_val(const struct ata_taskfile *tf);