linux-kernel - [PATCH v3 1/3] irqchip/loongson-eiointc: Skip handling if there is no pending irq

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Date: Thu, 18 Jan 2024 20:15:40 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Jiaxun Yang <jiaxun.yang@...goat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: linux-mips@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Sergey Shtylyov <s.shtylyov@....ru>,
	lvjianmin@...ngson.cn
Subject: [PATCH v3 1/3] irqchip/loongson-eiointc: Skip handling if there is no pending irq

There is one simple optimization in the interrupt dispatch function
eiointc_irq_dispatch. There are 256 IRQs supported for eiointc, eiointc
irq handler reads the bitmap and find pending irqs when irq happens.
So there are four times of consecutive iocsr_read64 operations for the
total 256 bits to find all pending irqs. If the pending bitmap is zero,
it means that there is no pending irq for the this irq bitmap range,
we can skip handling to avoid some useless operations such as clearing
hw ISR.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 drivers/irqchip/irq-loongson-eiointc.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
index 1623cd779175..6143adb1b73b 100644
--- a/drivers/irqchip/irq-loongson-eiointc.c
+++ b/drivers/irqchip/irq-loongson-eiointc.c
@@ -198,6 +198,17 @@ static void eiointc_irq_dispatch(struct irq_desc *desc)
 
 	for (i = 0; i < eiointc_priv[0]->vec_count / VEC_COUNT_PER_REG; i++) {
 		pending = iocsr_read64(EIOINTC_REG_ISR + (i << 3));
+
+		/*
+		 * Get pending eiointc irq from bitmap status, there are 4 times
+		 * consecutive iocsr_read64 operations for 256 IRQs.
+		 *
+		 * Skip handling if pending bitmap is zero
+		 */
+		if (!pending)
+			continue;
+
+		/* Clear the IRQs */
 		iocsr_write64(pending, EIOINTC_REG_ISR + (i << 3));
 		while (pending) {
 			int bit = __ffs(pending);
-- 
2.39.3