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From:   Vincent Chen <vincent.chen@sifive.com>
To:     daniel.lezcano@linaro.org, tglx@linutronix.de, palmer@dabbelt.com,
        paul.walmsley@sifive.com
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        vincent.chen@sifive.com
Subject: [PATCH] [RFC PATCH v1] clocksource: entend the max_delta_ns of timer-riscv andtimer-clint to ULONG_MAX
Date:   Tue,  8 Aug 2023 12:51:45 +0800
Message-Id: <20230808045145.3552312-1-vincent.chen@sifive.com>
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From: Vincentc Chen <vincent.chen@sifive.com>

When registering the riscv-timer or clint-timer as a clock_event device,
the driver needs to specify the value of max_delta_ticks. This value
directly influences the max_delta_ns, which signifies the maximum time
interval for configuring subsequent clock events. Currently, both
riscv-timer and clint-timer are set with a max_delta_ticks value of
0x7fff_ffff. When the timer operates at a high frequency, such as 1GHz,
this causes the system only can sleep for a short time. For the 1GHz
case, the sleep cannot exceed two seconds. To address this limitation,
refer to other timer implementations to extend it to 2^(bit-width of the
timer) - 1. Because the bit-width of $mtimecmp is 64bit, so this value
becomes ULONG_MAX (0xffff_ffff_ffff_ffff).

Signed-off-by: Vincentc Chen <vincent.chen@sifive.com>
---
 drivers/clocksource/timer-clint.c | 2 +-
 drivers/clocksource/timer-riscv.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index 9a55e733ae99..09fd292eb83d 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -131,7 +131,7 @@ static int clint_timer_starting_cpu(unsigned int cpu)
 	struct clock_event_device *ce = per_cpu_ptr(&clint_clock_event, cpu);
 
 	ce->cpumask = cpumask_of(cpu);
-	clockevents_config_and_register(ce, clint_timer_freq, 100, 0x7fffffff);
+	clockevents_config_and_register(ce, clint_timer_freq, 100, ULONG_MAX);
 
 	enable_percpu_irq(clint_timer_irq,
 			  irq_get_trigger_type(clint_timer_irq));
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index da3071b387eb..b25c91d41968 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -94,7 +94,7 @@ static int riscv_timer_starting_cpu(unsigned int cpu)
 	ce->irq = riscv_clock_event_irq;
 	if (riscv_timer_cannot_wake_cpu)
 		ce->features |= CLOCK_EVT_FEAT_C3STOP;
-	clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
+	clockevents_config_and_register(ce, riscv_timebase, 100, ULONG_MAX);
 
 	enable_percpu_irq(riscv_clock_event_irq,
 			  irq_get_trigger_type(riscv_clock_event_irq));
-- 
2.34.1