irq: mips: stop (ab)using handle_domain_irq()

On MIPS, the only user of handle_domain_irq() is octeon_irq_ciu3_ip2(),
which is called from the platform-specific plat_irq_dispatch() function
invoked from the early assembly code.

No other irqchip relevant to arch/mips uses handle_domain_irq():

* No other plat_irq_dispatch() function transitively calls
  handle_domain_irq().

* No other vectored IRQ dispatch function registered with
  set_vi_handler() calls handle_domain_irq().

* No chained irqchip handlers call handle_domain_irq(), which makes
  sense as this is meant to only be used by root irqchip handlers.

Currently octeon_irq_ciu3_ip2() passes NULL as the `regs` argument to
handle_domain_irq(), and as handle_domain_irq() will pass this to
set_irq_regs(), any invoked IRQ handlers will erroneously see a NULL
pt_regs if they call get_pt_regs().

Fix this by calling generic_handle_domain_irq() directly, and performing
the necessary irq_{enter,exit}() logic directly in
octeon_irq_ciu3_ip2(). At the same time, deselect HANDLE_DOMAIN_IRQ,
which subsequent patches will remove.

Other than the corrected behaviour of get_pt_regs(), there should be no
functional change as a result of this patch.

Fixes: ce210d35bb ("MIPS: OCTEON: Add support for OCTEON III interrupt controller.")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>

arch/mips/Kconfig

@@ -47,7 +47,6 @@ config MIPS
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_TIME_VSYSCALL
 	select GUP_GET_PTE_LOW_HIGH if CPU_MIPS32 && PHYS_ADDR_T_64BIT
-	select HANDLE_DOMAIN_IRQ
 	select HAVE_ARCH_COMPILER_H
 	select HAVE_ARCH_JUMP_LABEL
 	select HAVE_ARCH_KGDB if MIPS_FP_SUPPORT

arch/mips/cavium-octeon/octeon-irq.c

@@ -2609,7 +2609,10 @@ static void octeon_irq_ciu3_ip2(void)
 		else
 			hw = intsn;
 
-		ret = handle_domain_irq(domain, hw, NULL);
+		irq_enter();
+		ret = generic_handle_domain_irq(domain, hw);
+		irq_exit();
+
 		if (ret < 0) {
 			union cvmx_ciu3_iscx_w1c isc_w1c;
 			u64 isc_w1c_addr = ciu3_addr + CIU3_ISC_W1C(intsn);