IB/qib: Display correct value for number of contexts

A "fix" for a bug with the number of contexts on a single-port board
caused the calculation to be off by one, which causes problems with
the upper layers.  The same problem exists for number of free
contexts, which is also fixed here.
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib_init.c

@@ -102,6 +102,8 @@ void qib_set_ctxtcnt(struct qib_devdata *dd)
 		dd->cfgctxts = qib_cfgctxts;
 	else
 		dd->cfgctxts = dd->ctxtcnt;
+	dd->freectxts = (dd->first_user_ctxt > dd->cfgctxts) ? 0 :
+		dd->cfgctxts - dd->first_user_ctxt;
 }
 
 /*
@@ -402,7 +404,6 @@ static void enable_chip(struct qib_devdata *dd)
 		if (rcd)
 			dd->f_rcvctrl(rcd->ppd, rcvmask, i);
 	}
-	dd->freectxts = dd->cfgctxts - dd->first_user_ctxt;
 }
 
 static void verify_interrupt(unsigned long opaque)

drivers/infiniband/hw/qib/qib_sysfs.c

@@ -503,8 +503,11 @@ static ssize_t show_nctxts(struct device *device,
 	struct qib_devdata *dd = dd_from_dev(dev);
 
 	/* Return the number of user ports (contexts) available. */
-	return scnprintf(buf, PAGE_SIZE, "%u\n", dd->cfgctxts -
-		dd->first_user_ctxt);
+	/* The calculation below deals with a special case where
+	 * cfgctxts is set to 1 on a single-port board. */
+	return scnprintf(buf, PAGE_SIZE, "%u\n",
+			(dd->first_user_ctxt > dd->cfgctxts) ? 0 :
+			(dd->cfgctxts - dd->first_user_ctxt));
 }
 
 static ssize_t show_nfreectxts(struct device *device,