linux-kernel - [tip: timers/clocksource] clocksource/drivers/timer-sp804: Fix read_current_timer() issue when clock source is not registered

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Message-ID: <176416804655.498.15475479090310855080.tip-bot2@tip-bot2>
Date: Wed, 26 Nov 2025 14:40:46 -0000
From: "tip-bot2 for Stephen Eta Zhou" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: 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
 read_current_timer() issue when clock source is not registered

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

Commit-ID:     640594a04f119338019b0aeed70c7301216595b3
Gitweb:        https://git.kernel.org/tip/640594a04f119338019b0aeed70c7301216595b3
Author:        Stephen Eta Zhou <stephen.eta.zhou@...il.com>
AuthorDate:    Sun, 25 May 2025 16:43:28 +08:00
Committer:     Daniel Lezcano <daniel.lezcano@...aro.org>
CommitterDate: Wed, 26 Nov 2025 11:24:32 +01:00

clocksource/drivers/timer-sp804: Fix read_current_timer() issue when clock source is not registered

Register a valid read_current_timer() function for the
SP804 timer on ARM32.

On ARM32 platforms, when the SP804 timer is selected as the clocksource,
the driver does not register a valid read_current_timer() function.
As a result, features that rely on this API—such as rdseed—consistently
return incorrect values.

To fix this, a delay_timer structure is registered during the SP804
driver's initialization. The read_current_timer() function is implemented
using the existing sp804_read() logic, and the timer frequency is reused
from the already-initialized clocksource.

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/20250525-sp804-fix-read_current_timer-v4-1-87a9201fa4ec@gmail.com
---
 drivers/clocksource/timer-sp804.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/clocksource/timer-sp804.c b/drivers/clocksource/timer-sp804.c
index cd1916c..e82a95e 100644
--- a/drivers/clocksource/timer-sp804.c
+++ b/drivers/clocksource/timer-sp804.c
@@ -21,6 +21,10 @@
 #include <linux/of_irq.h>
 #include <linux/sched_clock.h>
 
+#ifdef CONFIG_ARM
+#include <linux/delay.h>
+#endif
+
 #include "timer-sp.h"
 
 /* Hisilicon 64-bit timer(a variant of ARM SP804) */
@@ -102,6 +106,23 @@ static u64 notrace sp804_read(void)
 	return ~readl_relaxed(sched_clkevt->value);
 }
 
+#ifdef CONFIG_ARM
+static struct delay_timer delay;
+static unsigned long sp804_read_delay_timer_read(void)
+{
+	return sp804_read();
+}
+
+static void sp804_register_delay_timer(int freq)
+{
+	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) {}
+#endif
+
 static int __init sp804_clocksource_and_sched_clock_init(void __iomem *base,
 							 const char *name,
 							 struct clk *clk,
@@ -114,6 +135,8 @@ 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);
@@ -318,6 +341,7 @@ static int __init sp804_of_init(struct device_node *np, struct sp804_timer *time
 		if (ret)
 			goto err;
 	}
+
 	initialized = true;
 
 	return 0;