linux-kernel - [tip: timers/clocksource] 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

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Message-ID: <176972232776.2495410.5417786508106401348.tip-bot2@tip-bot2>
Date: Thu, 29 Jan 2026 21:32:07 -0000
From: "tip-bot2 for Stephen Eta Zhou" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: kernel test robot <lkp@...el.com>,
 Stephen Eta Zhou <stephen.eta.zhou@...il.com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/clocksource] 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.

The following commit has been merged into the timers/clocksource branch of tip:

Commit-ID:     694921a93f3e3621e067afc545cedf6fe3b234a9
Gitweb:        https://git.kernel.org/tip/694921a93f3e3621e067afc545cedf6fe3b234a9
Author:        Stephen Eta Zhou <stephen.eta.zhou@...il.com>
AuthorDate:    Thu, 25 Dec 2025 16:16:31 +08:00
Committer:     Daniel Lezcano <daniel.lezcano@...aro.org>
CommitterDate: Tue, 20 Jan 2026 18:06:54 +01:00

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.

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@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512250520.APOMkYRQ-lkp@intel.com/
Signed-off-by: Stephen Eta Zhou <stephen.eta.zhou@...il.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
Link: https://patch.msgid.link/20251225-fix_timersp804-v2-1-a366d7157f58@gmail.com
---
 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 e82a95e..d698584 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);