[PATCH 6.19 093/781] clocksource/drivers/timer-sp804: Fix an Oops when read_current_timer is called on ARM32 platforms where the SP804 is not registered as the sched_clock.

Greg Kroah-Hartman
2026-02-25T01:28:31Z

From: Stephen Eta Zhou <stephen.eta.zhou@gmail.com>

[ Upstream commit 694921a93f3e3621e067afc545cedf6fe3b234a9 ]

On SP804, the delay timer shares the same clkevt instance with
sched_clock. On some platforms, when
sp804_clocksource_and_sched_clock_init is called with use_sched_clock
not set to 1, sched_clkevt is not properly initialized. However,
sp804_register_delay_timer is invoked unconditionally, and
read_current_timer() subsequently calls sp804_read on an uninitialized
sched_clkevt, leading to a kernel Oops when accessing
sched_clkevt->value.

Declare a dedicated clkevt instance exclusively for delay timer,
instead of sharing the same clkevt with sched_clock. This ensures
that read_current_timer continues to work correctly regardless of
whether SP804 is selected as the sched_clock.

Fixes: 640594a04f11 ("clocksource/drivers/timer-sp804: Fix read_current_timer() issue when clock source is not registered")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512250520.APOMkYRQ-lkp@intel.com/
Signed-off-by: Stephen Eta Zhou <stephen.eta.zhou@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://patch.msgid.link/20251225-fix_timersp804-v2-1-a366d7157f58@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/clocksource/timer-sp804.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/clocksource/timer-sp804.c b/drivers/clocksource/timer-sp804.c
index e82a95ea47247..d698584273596 100644
--- a/drivers/clocksource/timer-sp804.c
+++ b/drivers/clocksource/timer-sp804.c
@@ -106,21 +106,25 @@ static u64 notrace sp804_read(void)
return ~readl_relaxed(sched_clkevt->value);
}

+/* Register delay timer backed by the hardware counter */
#ifdef CONFIG_ARM
static struct delay_timer delay;
+static struct sp804_clkevt *delay_clkevt;
+
static unsigned long sp804_read_delay_timer_read(void)
{
- return sp804_read();
+ return ~readl_relaxed(delay_clkevt->value);
}

-static void sp804_register_delay_timer(int freq)
+static void sp804_register_delay_timer(struct sp804_clkevt *clk, int freq)
{
+ delay_clkevt = clk;
delay.freq = freq;
delay.read_current_timer = sp804_read_delay_timer_read;
register_current_timer_delay(&delay);
}
#else
-static inline void sp804_register_delay_timer(int freq) {}
+static inline void sp804_register_delay_timer(struct sp804_clkevt *clk, int freq) {}
#endif

static int __init sp804_clocksource_and_sched_clock_init(void __iomem *base,
@@ -135,8 +139,6 @@ static int __init sp804_clocksource_and_sched_clock_init(void __iomem *base,
if (rate < 0)
return -EINVAL;

- sp804_register_delay_timer(rate);
-
clkevt = sp804_clkevt_get(base);

writel(0, clkevt->ctrl);
@@ -152,6 +154,8 @@ static int __init sp804_clocksource_and_sched_clock_init(void __iomem *base,
clocksource_mmio_init(clkevt->value, name,
rate, 200, 32, clocksource_mmio_readl_down);

+ sp804_register_delay_timer(clkevt, rate);
+
if (use_sched_clock) {
sched_clkevt = clkevt;
sched_clock_register(sp804_read, 32, rate);
--
2.51.0