libata-pmp-prep: implement qc_defer helpers

Implement ap->nr_active_links (the number of links with active qcs),
ap->excl_link (pointer to link which can be used by ->qc_defer and is
cleared when a qc with ATA_QCFLAG_CLEAR_EXCL completes), and
ata_link_active().

These can be used by ->qc_defer() to implement proper command
exclusion.  This set of helpers seem enough for both sil24 (ATAPI
exclusion needed) and cmd-switching PMP.

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

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 1d3b0dccfb0a..5244723952c2 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -451,6 +451,7 @@ void ata_scsi_error(struct Scsi_Host *host)
 
                 ap->pflags |= ATA_PFLAG_EH_IN_PROGRESS;
                 ap->pflags &= ~ATA_PFLAG_EH_PENDING;
+                ap->excl_link = NULL;   /* don't maintain exclusion over EH */
 
                 spin_unlock_irqrestore(ap->lock, flags);
 
@@ -2474,6 +2475,10 @@ void ata_eh_finish(struct ata_port *ap)
                         }
                 }
         }
+
+        /* make sure nr_active_links is zero after EH */
+        WARN_ON(ap->nr_active_links);
+        ap->nr_active_links = 0;
 }
 
 /**