| Message ID | 20180618141933.3404739-1-arnd@arndb.de |
|---|---|
| State | Superseded |
| Headers | show |
| Series | firewire: ohci: stop using get_seconds() for BUS_TIME | expand |
Arnd Bergmann wrote: > The ohci driver uses the get_seconds() function to implement the 32-bit > CSR_BUS_TIME register. This was added in 2010 commit a48777e03ad5 > ("firewire: add CSR BUS_TIME support"). > > As get_seconds() returns a 32-bit value (on 32-bit architectures), it > seems like a good fit for that register, but it is also deprecated because > of the y2038/y2106 overflow problem, and should be replaced throughout > the kernel with either ktime_get_real_seconds() or ktime_get_seconds(). > > I'm using the latter here, which uses monotonic time. This has the > advantage of behaving better during concurrent settimeofday() updates > or leap second adjustments and won't overflow a 32-bit integer, but > the downside of using CLOCK_MONOTONIC instead of CLOCK_REALTIME is > that the observed values are not related to external clocks. > > If we instead need UTC but can live with clock jumps or overflows, > then we should use ktime_get_real_seconds() instead, retaining the > existing behavior. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> Reviewed-By: Clemens Ladisch <clemens@ladisch.de> > --- > drivers/firewire/ohci.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c > index 45c048751f3b..5125841ea338 100644 > --- a/drivers/firewire/ohci.c > +++ b/drivers/firewire/ohci.c > @@ -1765,7 +1765,7 @@ static u32 update_bus_time(struct fw_ohci *ohci) > > if (unlikely(!ohci->bus_time_running)) { > reg_write(ohci, OHCI1394_IntMaskSet, OHCI1394_cycle64Seconds); > - ohci->bus_time = (lower_32_bits(get_seconds()) & ~0x7f) | > + ohci->bus_time = (lower_32_bits(ktime_get_seconds()) & ~0x7f) | > (cycle_time_seconds & 0x40); > ohci->bus_time_running = true; > }
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c index 45c048751f3b..5125841ea338 100644 --- a/drivers/firewire/ohci.c +++ b/drivers/firewire/ohci.c @@ -1765,7 +1765,7 @@ static u32 update_bus_time(struct fw_ohci *ohci) if (unlikely(!ohci->bus_time_running)) { reg_write(ohci, OHCI1394_IntMaskSet, OHCI1394_cycle64Seconds); - ohci->bus_time = (lower_32_bits(get_seconds()) & ~0x7f) | + ohci->bus_time = (lower_32_bits(ktime_get_seconds()) & ~0x7f) | (cycle_time_seconds & 0x40); ohci->bus_time_running = true; }
The ohci driver uses the get_seconds() function to implement the 32-bit CSR_BUS_TIME register. This was added in 2010 commit a48777e03ad5 ("firewire: add CSR BUS_TIME support"). As get_seconds() returns a 32-bit value (on 32-bit architectures), it seems like a good fit for that register, but it is also deprecated because of the y2038/y2106 overflow problem, and should be replaced throughout the kernel with either ktime_get_real_seconds() or ktime_get_seconds(). I'm using the latter here, which uses monotonic time. This has the advantage of behaving better during concurrent settimeofday() updates or leap second adjustments and won't overflow a 32-bit integer, but the downside of using CLOCK_MONOTONIC instead of CLOCK_REALTIME is that the observed values are not related to external clocks. If we instead need UTC but can live with clock jumps or overflows, then we should use ktime_get_real_seconds() instead, retaining the existing behavior. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- drivers/firewire/ohci.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.9.0