[SCSI] isci: Fix interrupt coalescing assumption of active TCs

We always assign a dummy task context to a port in order to address a
silicon issue. We have 4 ports per controller. So when idle, there are always
exactly 4 TCs "active". The adaptive interrupt coalescing code uses number of
active TCs to figure out the coalescing values. However, we never hit "0" TCs
because of the 4 dummy TCs. Putting in fix so that we calculate this correctly.

Reported-by: Dan Melnic <dan@seamicro.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/isci/host.c b/drivers/scsi/isci/host.c
index d4daa0f..ab026a5 100644 (file)
--- a/drivers/scsi/isci/host.c
+++ b/drivers/scsi/isci/host.c
@@ -1122,10 +1122,16 @@ void isci_host_completion_routine(unsigned long data)
        sci_controller_completion_handler(ihost);
        spin_unlock_irq(&ihost->scic_lock);
 
-       /* the coalesence timeout doubles at each encoding step, so
+       /*
+        * we subtract SCI_MAX_PORTS to account for the number of dummy TCs
+        * issued for hardware issue workaround
+        */
+       active = isci_tci_active(ihost) - SCI_MAX_PORTS;
+
+       /*
+        * the coalesence timeout doubles at each encoding step, so
         * update it based on the ilog2 value of the outstanding requests
         */
-       active = isci_tci_active(ihost);
        writel(SMU_ICC_GEN_VAL(NUMBER, active) |
               SMU_ICC_GEN_VAL(TIMER, ISCI_COALESCE_BASE + ilog2(active)),
               &ihost->smu_registers->interrupt_coalesce_control);