[PATCH] IB/ipath: fix lost interrupts on HT-400

Do an extra check to see if in-memory tail changed while processing packets,
and if so, going back through the loop again (but only once per call to
ipath_kreceive()).  In practice, this seems to be enough to guarantee that if
we crossed the clearing of an interrupt at start of ipath_intr with a
scheduled tail register update, that we'll process the "extra" packet that
lost the interrupt because we cleared it just as it was about to arrive.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Bryan O'Sullivan <bryan.osullivan@qlogic.com>
Cc: "Michael S. Tsirkin" <mst@mellanox.co.il>
Cc: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 36 insertions, 17 deletions

diff --git a/drivers/infiniband/hw/ipath/ipath_driver.c b/drivers/infiniband/hw/ipath/ipath_driver.c
index e2b0bc8ebaf4..66b41ecf898b 100644
--- a/drivers/infiniband/hw/ipath/ipath_driver.c
+++ b/drivers/infiniband/hw/ipath/ipath_driver.c
@@ -870,7 +870,7 @@ void ipath_kreceive(struct ipath_devdata *dd)
         const u32 maxcnt = dd->ipath_rcvhdrcnt * rsize; /* words */
         u32 etail = -1, l, hdrqtail;
         struct ips_message_header *hdr;
-        u32 eflags, i, etype, tlen, pkttot = 0, updegr=0;
+        u32 eflags, i, etype, tlen, pkttot = 0, updegr=0, reloop=0;
         static u64 totcalls;    /* stats, may eventually remove */
         char emsg[128];
 
@@ -885,9 +885,11 @@ void ipath_kreceive(struct ipath_devdata *dd)
                 goto bail;
 
         l = dd->ipath_port0head;
-        if (l == (u32)le64_to_cpu(*dd->ipath_hdrqtailptr))
+        hdrqtail = (u32) le64_to_cpu(*dd->ipath_hdrqtailptr);
+        if (l == hdrqtail)
                 goto done;
 
+reloop:
         /* read only once at start for performance */
         hdrqtail = (u32)le64_to_cpu(*dd->ipath_hdrqtailptr);
 
@@ -1011,7 +1013,7 @@ void ipath_kreceive(struct ipath_devdata *dd)
                  */
                 if (l == hdrqtail || (i && !(i&0xf))) {
                         u64 lval;
-                        if (l == hdrqtail) /* want interrupt only on last */
+                        if (l == hdrqtail) /* PE-800 interrupt only on last */
                                 lval = dd->ipath_rhdrhead_intr_off | l;
                         else
                                 lval = l;
@@ -1024,6 +1026,23 @@ void ipath_kreceive(struct ipath_devdata *dd)
                 }
         }
 
+        if (!dd->ipath_rhdrhead_intr_off && !reloop) {
+                /* HT-400 workaround; we can have a race clearing chip
+                 * interrupt with another interrupt about to be delivered,
+                 * and can clear it before it is delivered on the GPIO
+                 * workaround.  By doing the extra check here for the
+                 * in-memory tail register updating while we were doing
+                 * earlier packets, we "almost" guarantee we have covered
+                 * that case.
+                 */
+                u32 hqtail = (u32)le64_to_cpu(*dd->ipath_hdrqtailptr);
+                if (hqtail != hdrqtail) {
+                        hdrqtail = hqtail;
+                        reloop = 1; /* loop 1 extra time at most */
+                        goto reloop;
+                }
+        }
+
         pkttot += i;
 
         dd->ipath_port0head = l;
diff --git a/drivers/infiniband/hw/ipath/ipath_intr.c b/drivers/infiniband/hw/ipath/ipath_intr.c
index bad20a395265..83b51ed89527 100644
--- a/drivers/infiniband/hw/ipath/ipath_intr.c
+++ b/drivers/infiniband/hw/ipath/ipath_intr.c
@@ -766,7 +766,7 @@ irqreturn_t ipath_intr(int irq, void *data, struct pt_regs *regs)
         u32 istat, chk0rcv = 0;
         ipath_err_t estat = 0;
         irqreturn_t ret;
-        u32 p0bits, oldhead;
+        u32 oldhead, curtail;
         static unsigned unexpected = 0;
         static const u32 port0rbits = (1U<<INFINIPATH_I_RCVAVAIL_SHIFT) |
                  (1U<<INFINIPATH_I_RCVURG_SHIFT);
@@ -809,15 +809,16 @@ irqreturn_t ipath_intr(int irq, void *data, struct pt_regs *regs)
          * lose intr for later packets that arrive while we are processing.
          */
         oldhead = dd->ipath_port0head;
-        if (oldhead != (u32) le64_to_cpu(*dd->ipath_hdrqtailptr)) {
+        curtail = (u32)le64_to_cpu(*dd->ipath_hdrqtailptr);
+        if (oldhead != curtail) {
                 if (dd->ipath_flags & IPATH_GPIO_INTR) {
                         ipath_write_kreg(dd, dd->ipath_kregs->kr_gpio_clear,
                                          (u64) (1 << 2));
-                        p0bits = port0rbits | INFINIPATH_I_GPIO;
+                        istat = port0rbits | INFINIPATH_I_GPIO;
                 }
                 else
-                        p0bits = port0rbits;
-                ipath_write_kreg(dd, dd->ipath_kregs->kr_intclear, p0bits);
+                        istat = port0rbits;
+                ipath_write_kreg(dd, dd->ipath_kregs->kr_intclear, istat);
                 ipath_kreceive(dd);
                 if (oldhead != dd->ipath_port0head) {
                         ipath_stats.sps_fastrcvint++;
@@ -827,7 +828,6 @@ irqreturn_t ipath_intr(int irq, void *data, struct pt_regs *regs)
         }
 
         istat = ipath_read_kreg32(dd, dd->ipath_kregs->kr_intstatus);
-        p0bits = port0rbits;
 
         if (unlikely(!istat)) {
                 ipath_stats.sps_nullintr++;
@@ -890,19 +890,19 @@ irqreturn_t ipath_intr(int irq, void *data, struct pt_regs *regs)
                 else {
                         /* Clear GPIO status bit 2 */
                         ipath_write_kreg(dd, dd->ipath_kregs->kr_gpio_clear,
-                                         (u64) (1 << 2));
-                        p0bits |= INFINIPATH_I_GPIO;
+                                        (u64) (1 << 2));
                         chk0rcv = 1;
                 }
         }
-        chk0rcv |= istat & p0bits;
+        chk0rcv |= istat & port0rbits;
 
         /*
-         * clear the ones we will deal with on this round
-         * We clear it early, mostly for receive interrupts, so we
-         * know the chip will have seen this by the time we process
-         * the queue, and will re-interrupt if necessary.  The processor
-         * itself won't take the interrupt again until we return.
+         * Clear the interrupt bits we found set, unless they are receive
+         * related, in which case we already cleared them above, and don't
+         * want to clear them again, because we might lose an interrupt.
+         * Clear it early, so we "know" know the chip will have seen this by
+         * the time we process the queue, and will re-interrupt if necessary.
+         * The processor itself won't take the interrupt again until we return.
          */
         ipath_write_kreg(dd, dd->ipath_kregs->kr_intclear, istat);