[tip: irq/drivers] LoongArch: Override arch_dynirq_lower_bound to reserve LPC IRQs

["tip-bot2 for Icenowy Zheng" <tip-bot2@linutronix.de>]

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

Commit-ID:     dc30127cd050dbc9d8452846ee7fa6692a1093d2
Gitweb:        https://git.kernel.org/tip/dc30127cd050dbc9d8452846ee7fa6692a1093d2
Author:        Icenowy Zheng <zhengxingda@iscas.ac.cn>
AuthorDate:    Sat, 21 Mar 2026 17:20:28 +08:00
Committer:     Thomas Gleixner <tglx@kernel.org>
CommitterDate: Thu, 26 Mar 2026 16:15:03 +01:00

LoongArch: Override arch_dynirq_lower_bound to reserve LPC IRQs

Loongson 7A PCH chips all contain a LPC controller, which is used in
some devices to connect legacy ISA devices (e.g. 8259 PS/2 controller).

The LPC irqchip driver will register LPC interrupts at the fixed range
0~15, and the PCH PIC irqchip driver uses dynamic allocation. However the
LPC interrupt numbers are currently not exempted from dynamic allocation.

The current setup work by accident because the LPC interrupt controller is
the first consumer of PIC interrupt controller, and the PIC interrupt
number is allocated after LPC interrupts are registered. Such setup is
fragile and will stop to work when the LPC irqchip driver is reworked.

Override arch_dynirq_lower_bound() to reserve LPC interrupts from dynamic
allocation, to prevent interrupt number collision and allow rework of the
LPC irqchip driver.

Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/20260321092032.3502701-3-zhengxingda@iscas.ac.cn
---
 arch/loongarch/kernel/irq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/loongarch/kernel/irq.c b/arch/loongarch/kernel/irq.c
index 80946ca..7bf68a7 100644
--- a/arch/loongarch/kernel/irq.c
+++ b/arch/loongarch/kernel/irq.c
@@ -11,6 +11,7 @@
 #include <linux/irqchip.h>
 #include <linux/kernel_stat.h>
 #include <linux/proc_fs.h>
+#include <linux/minmax.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
@@ -99,6 +100,11 @@ int __init arch_probe_nr_irqs(void)
 	return NR_IRQS_LEGACY;
 }
 
+unsigned int arch_dynirq_lower_bound(unsigned int from)
+{
+	return MAX(from, NR_IRQS_LEGACY);
+}
+
 void __init init_IRQ(void)
 {
 	int i;