linux-kernel - [PATCH 1/2] clocksource: timer-riscv: Don't enable/disable timer interrupt

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Message-Id: <20230710131902.1459180-2-apatel@ventanamicro.com>
Date:   Mon, 10 Jul 2023 18:49:01 +0530
From:   Anup Patel <apatel@...tanamicro.com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Atish Patra <atishp@...shpatra.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Conor Dooley <conor@...nel.org>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Anup Patel <apatel@...tanamicro.com>
Subject: [PATCH 1/2] clocksource: timer-riscv: Don't enable/disable timer interrupt

Currently, we enable/disable timer interrupt at runtime to start/stop
timer events. This makes timer interrupt state go out-of-sync with
the Linux interrupt subsystem.

To address the above issue, we can stop a per-HART timer interrupt
by setting U64_MAX in timecmp CSR (or sbi_set_timer()) at the time
of handling timer interrupt.

Signed-off-by: Anup Patel <apatel@...tanamicro.com>
---
 drivers/clocksource/timer-riscv.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index da3071b387eb..f2ea2b3d2d43 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -22,6 +22,7 @@
 #include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/interrupt.h>
 #include <linux/of_irq.h>
+#include <linux/limits.h>
 #include <clocksource/timer-riscv.h>
 #include <asm/smp.h>
 #include <asm/hwcap.h>
@@ -31,12 +32,22 @@
 static DEFINE_STATIC_KEY_FALSE(riscv_sstc_available);
 static bool riscv_timer_cannot_wake_cpu;
 
+static void riscv_clock_event_stop(void)
+{
+	if (static_branch_likely(&riscv_sstc_available)) {
+		csr_write(CSR_STIMECMP, ULONG_MAX);
+		if (IS_ENABLED(CONFIG_32BIT))
+			csr_write(CSR_STIMECMPH, ULONG_MAX);
+	} else {
+		sbi_set_timer(U64_MAX);
+	}
+}
+
 static int riscv_clock_next_event(unsigned long delta,
 		struct clock_event_device *ce)
 {
 	u64 next_tval = get_cycles64() + delta;
 
-	csr_set(CSR_IE, IE_TIE);
 	if (static_branch_likely(&riscv_sstc_available)) {
 #if defined(CONFIG_32BIT)
 		csr_write(CSR_STIMECMP, next_tval & 0xFFFFFFFF);
@@ -119,7 +130,7 @@ static irqreturn_t riscv_timer_interrupt(int irq, void *dev_id)
 {
 	struct clock_event_device *evdev = this_cpu_ptr(&riscv_clock_event);
 
-	csr_clear(CSR_IE, IE_TIE);
+	riscv_clock_event_stop();
 	evdev->event_handler(evdev);
 
 	return IRQ_HANDLED;
-- 
2.34.1