realtek: backport MIPS GIC patch

Upstream has gained support for forced affinity settings in the MIPS
GIC interrupt controller. This is needed to enable the Otto timer on
the RTL931x platform. See

https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/
commit/?id=2250db8628a0d8293ad2e0671138b848a185fba1

Signed-off-by: Markus Stockhausen <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/19205
Signed-off-by: Robert Marko <[email protected]>

target/linux/realtek/patches-6.12/302-6.17-irqchip-mips-gic-forced-affinity.patch

@@ -0,0 +1,47 @@
+From 2250db8628a0d8293ad2e0671138b848a185fba1 Mon Sep 17 00:00:00 2001
+From: Markus Stockhausen <[email protected]>
+Date: Sat, 21 Jun 2025 01:49:51 -0400
+Subject: irqchip/mips-gic: Allow forced affinity
+
+Devices of the Realtek MIPS Otto platform use the official rtl-otto-timer
+as clock event generator and CPU clocksource. It is registered for each CPU
+startup via cpuhp_setup_state() and forces the affinity of the clockevent
+interrupts to the appropriate CPU via irq_force_affinity().
+
+On the "smaller" devices with a vendor specific interrupt controller
+(supported by irq-realtek-rtl) the registration works fine. The "larger"
+RTL931x series is based on a MIPS interAptiv dual core with a MIPS GIC
+controller. Interrupt routing setup is cancelled because gic_set_affinity()
+does not accept the current (not yet online) CPU as a target.
+
+Relax the checks by evaluating the force parameter that is provided for
+exactly this purpose like in other drivers. With this the affinity can be
+set as follows:
+
+ - force = false: allow to set affinity to any online cpu
+ - force = true:  allow to set affinity to any cpu
+
+Co-developed-by: Sebastian Gottschall <[email protected]>
+Signed-off-by: Sebastian Gottschall <[email protected]>
+Signed-off-by: Markus Stockhausen <[email protected]>
+Signed-off-by: Thomas Gleixner <[email protected]>
+Link: https://lore.kernel.org/all/[email protected]
+---
+ drivers/irqchip/irq-mips-gic.c | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+--- a/drivers/irqchip/irq-mips-gic.c
++++ b/drivers/irqchip/irq-mips-gic.c
+@@ -263,7 +263,11 @@ static int gic_set_affinity(struct irq_d
+ 	unsigned long flags;
+ 	unsigned int cpu;
+ 
+-	cpu = cpumask_first_and(cpumask, cpu_online_mask);
++	if (force)
++		cpu = cpumask_first(cpumask);
++	else
++		cpu = cpumask_first_and(cpumask, cpu_online_mask);
++
+ 	if (cpu >= NR_CPUS)
+ 		return -EINVAL;
+