linux-kernel - [PATCH 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL

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Date:   Mon, 17 Aug 2020 20:24:15 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>
CC:     Marc Zyngier <maz@...nel.org>, Steven Price <steven.price@....com>,
        "Andrew Jones" <drjones@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>, James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        <wanghaibin.wang@...wei.com>, Keqian Zhu <zhukeqian1@...wei.com>
Subject: [PATCH 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

ARM virtual counter supports event stream, it can only trigger an event
when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0 changes,
so the actual period of event stream is 2^(cntkctl_evnti + 1). For example,
when the trigger bit is 0, then virtual counter trigger an event for every
two cycles.

Signed-off-by: Marc Zyngier <maz@...nel.org>
Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
---
 drivers/clocksource/arm_arch_timer.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6e11c60..4140a37 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -794,10 +794,14 @@ static void arch_timer_configure_evtstream(void)
 {
 	int evt_stream_div, pos;
 
-	/* Find the closest power of two to the divisor */
-	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+	/*
+	 * Find the closest power of two to the divisor. As the event
+	 * stream can at most be generated at half the frequency of the
+	 * counter, use half the frequency when computing the divider.
+	 */
+	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ / 2;
 	pos = fls(evt_stream_div);
-	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+	if ((pos == 1) || (pos > 1 && !(evt_stream_div & (1 << (pos - 2)))))
 		pos--;
 	/* enable event stream */
 	arch_timer_evtstrm_enable(min(pos, 15));
-- 
1.8.3.1