linux-kernel - [PATCH] irqchip/sifive-plic: Avoid clearing the per-hart enable bits

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Message-Id: <20230717185841.1294425-1-samuel.holland@sifive.com>
Date:   Mon, 17 Jul 2023 11:58:40 -0700
From:   Samuel Holland <samuel.holland@...ive.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Samuel Holland <samuel.holland@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Samuel Holland <samuel@...lland.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH] irqchip/sifive-plic: Avoid clearing the per-hart enable bits

Writes to the PLIC completion register are ignored if the enable bit for
that (interrupt, hart) combination is cleared. This leaves the interrupt
in a claimed state, preventing it from being triggered again.

Originally, the enable bit was cleared in the .irq_mask operation, and
commit 69ea463021be ("irqchip/sifive-plic: Fixup EOI failed when masked")
added a workaround for this issue. Later, commit a1706a1c5062
("irqchip/sifive-plic: Separate the enable and mask operations") moved
toggling the enable bit to the .irq_enable/.irq_disable operations and
removed the workaround.

However, there are still places where .irq_disable can be called from
inside the hard IRQ handler, for example in irq_pm_check_wakeup(). As a
result, this issue causes an interrupt to get stuck in a claimed state
after being used to wake the system from s2idle.

There is no real benefit to implementing the .irq_enable/.irq_disable
operations using the enable bits. In fact, the existing mask/unmask
implementation using the threshold register is already more efficient,
as it requires no read/modify/write cycles. So let's leave the enable
bits set for the lifetime of the IRQ, using them only to control its
affinity.

Fixes: a1706a1c5062 ("irqchip/sifive-plic: Separate the enable and mask operations")
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

 drivers/irqchip/irq-sifive-plic.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index e1484905b7bd..c2673fdad8e5 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -120,12 +120,14 @@ static inline void plic_irq_toggle(const struct cpumask *mask,
 	}
 }

-static void plic_irq_enable(struct irq_data *d)
+static unsigned int plic_irq_startup(struct irq_data *d)
 {
 	plic_irq_toggle(irq_data_get_effective_affinity_mask(d), d, 1);
+
+	return 0;
 }

-static void plic_irq_disable(struct irq_data *d)
+static void plic_irq_shutdown(struct irq_data *d)
 {
 	plic_irq_toggle(irq_data_get_effective_affinity_mask(d), d, 0);
 }
@@ -169,12 +171,12 @@ static int plic_set_affinity(struct irq_data *d,
 	if (cpu >= nr_cpu_ids)
 		return -EINVAL;

-	plic_irq_disable(d);
+	plic_irq_shutdown(d);

 	irq_data_update_effective_affinity(d, cpumask_of(cpu));

-	if (!irqd_irq_disabled(d))
-		plic_irq_enable(d);
+	if (irqd_is_started(d))
+		plic_irq_startup(d);

 	return IRQ_SET_MASK_OK_DONE;
 }
@@ -182,8 +184,8 @@ static int plic_set_affinity(struct irq_data *d,

 static struct irq_chip plic_edge_chip = {
 	.name		= "SiFive PLIC",
-	.irq_enable	= plic_irq_enable,
-	.irq_disable	= plic_irq_disable,
+	.irq_startup	= plic_irq_startup,
+	.irq_shutdown	= plic_irq_shutdown,
 	.irq_ack	= plic_irq_eoi,
 	.irq_mask	= plic_irq_mask,
 	.irq_unmask	= plic_irq_unmask,
@@ -197,8 +199,8 @@ static struct irq_chip plic_edge_chip = {

 static struct irq_chip plic_chip = {
 	.name		= "SiFive PLIC",
-	.irq_enable	= plic_irq_enable,
-	.irq_disable	= plic_irq_disable,
+	.irq_startup	= plic_irq_startup,
+	.irq_shutdown	= plic_irq_shutdown,
 	.irq_mask	= plic_irq_mask,
 	.irq_unmask	= plic_irq_unmask,
 	.irq_eoi	= plic_irq_eoi,
-- 
2.40.1