linux-kernel - [PATCH v5 2/3] irqchip/loongson-eiointc: Skip handling if there is no pending irq

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Message-Id: <20240130082722.2912576-3-maobibo@loongson.cn>
Date: Tue, 30 Jan 2024 16:27:21 +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,
	Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH v5 2/3] irqchip/loongson-eiointc: Skip handling if there is no pending irq

It is one simple optimization in the interrupt dispatch function
eiointc_irq_dispatch(). There are 256 IRQs supported for eiointc on
Loongson-3A5000 and Loongson-2K2000 platform, 128 IRQs on Loongson-2K0500
platform, eiointc irq handler reads the bitmap and find pending irqs
when irq happens. So there are several consecutive iocsr_read64
operations for the all 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>
Acked-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 drivers/irqchip/irq-loongson-eiointc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/irqchip/irq-loongson-eiointc.c b/drivers/irqchip/irq-loongson-eiointc.c
index b3736bdd4b9f..6a71a8c29ac7 100644
--- a/drivers/irqchip/irq-loongson-eiointc.c
+++ b/drivers/irqchip/irq-loongson-eiointc.c
@@ -198,6 +198,12 @@ 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));
+
+		/* 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