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

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/loongarch/kernel/irq.c b/arch/loongarch/kernel/irq.c
index 80946cafaec1..7bf68a7a5f4b 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;