1 files changed, 49 insertions, 3 deletions

diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index 6610d2d38802..d6ba897b2197 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -192,6 +192,7 @@ struct fw_ohci {
         bool use_dualbuffer;
         bool old_uninorth;
         bool bus_reset_packet_quirk;
+        bool iso_cycle_timer_quirk;
 
         /*
          * Spinlock for accessing fw_ohci data.  Never call out of
@@ -1794,14 +1795,57 @@ static int ohci_enable_phys_dma(struct fw_card *card,
 #endif /* CONFIG_FIREWIRE_OHCI_REMOTE_DMA */
 }
 
+static inline u32 cycle_timer_ticks(u32 cycle_timer)
+{
+        u32 ticks;
+
+        ticks = cycle_timer & 0xfff;
+        ticks += 3072 * ((cycle_timer >> 12) & 0x1fff);
+        ticks += (3072 * 8000) * (cycle_timer >> 25);
+        return ticks;
+}
+
 static u64 ohci_get_bus_time(struct fw_card *card)
 {
         struct fw_ohci *ohci = fw_ohci(card);
-        u32 cycle_time;
+        u32 c0, c1, c2;
+        u32 t0, t1, t2;
+        s32 diff01, diff12;
         u64 bus_time;
 
-        cycle_time = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
-        bus_time = ((u64)atomic_read(&ohci->bus_seconds) << 32) | cycle_time;
+        if (!ohci->iso_cycle_timer_quirk) {
+                c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
+        } else {
+                /*
+                 * VIA controllers have two bugs when updating the iso cycle
+                 * timer register:
+                 * 1) When the lowest six bits are wrapping around to zero,
+                 *    a read that happens at the same time will return garbage
+                 *    in the lowest ten bits.
+                 * 2) When the cycleOffset field wraps around to zero, the
+                 *    cycleCount field is not incremented for about 60 ns.
+                 *
+                 * To catch these, we read the register three times and ensure
+                 * that the difference between each two consecutive reads is
+                 * approximately the same, i.e., less than twice the other.
+                 * Furthermore, any negative difference indicates an error.
+                 * (A PCI read should take at least 20 ticks of the 24.576 MHz
+                 * timer to execute, so we have enough precision to compute the
+                 * ratio of the differences.)
+                 */
+                do {
+                        c0 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
+                        c1 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
+                        c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
+                        t0 = cycle_timer_ticks(c0);
+                        t1 = cycle_timer_ticks(c1);
+                        t2 = cycle_timer_ticks(c2);
+                        diff01 = t1 - t0;
+                        diff12 = t2 - t1;
+                } while (diff01 <= 0 || diff12 <= 0 ||
+                         diff01 / diff12 >= 2 || diff12 / diff01 >= 2);
+        }
+        bus_time = ((u64)atomic_read(&ohci->bus_seconds) << 32) | c2;
 
         return bus_time;
 }
@@ -2498,6 +2542,8 @@ static int __devinit pci_probe(struct pci_dev *dev,
 #endif
         ohci->bus_reset_packet_quirk = dev->vendor == PCI_VENDOR_ID_TI;
 
+        ohci->iso_cycle_timer_quirk = dev->vendor == PCI_VENDOR_ID_VIA;
+
         ar_context_init(&ohci->ar_request_ctx, ohci,
                         OHCI1394_AsReqRcvContextControlSet);