From: Arnd Bergmann <arnd@arndb.de>
To: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: y2038@lists.linaro.org, Arnd Bergmann <arnd@arndb.de>,
Hector Martin <marcan@marcan.st>,
Mark Rutland <mark.rutland@arm.com>,
Ingo Molnar <mingo@kernel.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux1394-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: [PATCH] firewire: ohci: stop using get_seconds() for BUS_TIME
Date: Mon, 18 Jun 2018 16:19:24 +0200 [thread overview]
Message-ID: <20180618141933.3404739-1-arnd@arndb.de> (raw)
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(-)
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;
}
--
2.9.0
next reply other threads:[~2018-06-18 14:20 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-18 14:19 Arnd Bergmann [this message]
2018-06-19 6:26 ` [PATCH] firewire: ohci: stop using get_seconds() for BUS_TIME Clemens Ladisch
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