firewire: get_cycle_timer optimization and cleanup
ohci: Break out of the retry loop if too many attempts were necessary.
This may theoretically happen if the chip is fatally defective or if the
get_cycle_timer ioctl was performed after a CardBus controller was
ejected.
Also micro-optimize the loop by re-using the last two register reads in
the next iteration, remove a questionable inline keyword, and shuffle a
comment around.
core: ioctl_get_cycle_timer() is always called with interrupts on,
therefore local_irq_save() can be replaced by local_irq_disable().
Disabled local IRQs imply disabled preemption, hence preempt_disable()
can be removed.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index bf5e112..c3eb471 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -1795,60 +1795,61 @@
#endif /* CONFIG_FIREWIRE_OHCI_REMOTE_DMA */
}
-static inline u32 cycle_timer_ticks(u32 cycle_timer)
+static 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;
}
+/*
+ * Some controllers exhibit one or more of the following bugs when updating the
+ * iso cycle timer register:
+ * - 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.
+ * - When the cycleOffset field wraps around to zero, the cycleCount field is
+ * not incremented for about 60 ns.
+ * - Occasionally, the entire register reads zero.
+ *
+ * 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.)
+ */
static u64 ohci_get_bus_time(struct fw_card *card)
{
struct fw_ohci *ohci = fw_ohci(card);
u32 c0, c1, c2;
u32 t0, t1, t2;
s32 diff01, diff12;
- u64 bus_time;
+ int i;
- if (!ohci->iso_cycle_timer_quirk) {
+ c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
+
+ if (ohci->iso_cycle_timer_quirk) {
+ i = 0;
+ c1 = c2;
c2 = reg_read(ohci, OHCI1394_IsochronousCycleTimer);
- } else {
- /*
- * Some controllers exhibit one or more of the following bugs
- * when updating the iso cycle timer register:
- * - 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.
- * - When the cycleOffset field wraps around to zero, the
- * cycleCount field is not incremented for about 60 ns.
- * - Occasionally, the entire register reads zero.
- *
- * 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);
+ c0 = c1;
+ c1 = c2;
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);
+ } while ((diff01 <= 0 || diff12 <= 0 ||
+ diff01 / diff12 >= 2 || diff12 / diff01 >= 2)
+ && i++ < 20);
}
- bus_time = ((u64)atomic_read(&ohci->bus_seconds) << 32) | c2;
- return bus_time;
+ return ((u64)atomic_read(&ohci->bus_seconds) << 32) | c2;
}
static void copy_iso_headers(struct iso_context *ctx, void *p)