FROMLIST: arm: Mark the recheduling IPI as raw interrupt

Flag the rescheduling IPI as 'raw', making sure such interrupt
skips both tick management  and irqtime accounting.

Bug: 191808738
Link: https://lore.kernel.org/lkml/20201124141449.572446-5-maz@kernel.org/
Change-Id: Ia9c2b989621eef6f49a1c30a08302a448ae286e6
Signed-off-by: Marc Zyngier <maz@kernel.org>
[minor port to 5.10]
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>

arch/arm/Kconfig

@@ -51,6 +51,7 @@ config ARM
 	select GENERIC_ATOMIC64 if CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI
 	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
 	select GENERIC_IRQ_IPI if SMP
+	select ARCH_WANTS_IRQ_RAW if GENERIC_IRQ_IPI
 	select GENERIC_CPU_AUTOPROBE
 	select GENERIC_EARLY_IOREMAP
 	select GENERIC_IDLE_POLL_SETUP

arch/arm/kernel/smp.c

@@ -742,6 +742,10 @@ void __init set_smp_ipi_range(int ipi_base, int n)
 
 		ipi_desc[i] = irq_to_desc(ipi_base + i);
 		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
+
+		/* The recheduling IPI is special... */
+		if (i == IPI_RESCHEDULE)
+			__irq_modify_status(ipi_base + i, 0, IRQ_RAW, ~0);
 	}
 
 	ipi_irq_base = ipi_base;