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@loongson.cn>
Acked-by: Huacai Chen <chenhuacai@loongson.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

The following commit has been merged into the irq/core branch of tip:

Commit-ID:     3eece72ded7f67776731709702f3d1b9893b6a4f
Gitweb:        https://git.kernel.org/tip/3eece72ded7f67776731709702f3d1b9893b6a4f
Author:        Bibo Mao <maobibo@loongson.cn>
AuthorDate:    Tue, 30 Jan 2024 16:27:21 +08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 13 Feb 2024 10:53:14 +01:00

irqchip/loongson-eiointc: Skip handling if there is no pending interrupt

eiointc_irq_dispatch() iterates over the pending bit registers of the
interrupt controller and evaluates the result even if there is no interrupt
pending in a particular 64bit chunk.

Skip handling and especially the pointless write back for clearing the
non-pending bits if a chunk is empty.

[ tglx: Massaged changelog ]

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/r/20240130082722.2912576-3-maobibo@loongson.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 1623cd7..fad22e2 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);