[PATCH RFC 3/2] ARM: improve arch_irq_work_has_interrupt()

[Russell King - ARM Linux]

Following on from the previous patch, I think this makes more sense to
determine whether we can support IRQ work interrupts.

Whether we can support them or not depends on two things:

(a) whether the kernel has support for receiving IPIs
(b) whether it's possible to send an IPI to CPUs including the raising CPU.

(a) is a function of how the kernel is built - and in the case of ARM, it
depends whether the kernel is built with SMP enabled or not.
(b) is a property of the interrupt controller.

It hasn't ever been a function of the CPU or architecture.

Commit 059e232089e4 ("irqchip/gic: Allow self-SGIs for SMP on UP
configurations") changes the GIC IPI code such that we can raise
SGIs on uniprocessor systems running on a SMP kernel, which means
we can support IRQ work interrupts here as well.

So, we shouldn't be using cpu_smp() (or its previous is_smp() here
at all.  Use a flag to indicate whether we can IPI and use that to
indicate whether we support irq work interrupts.

Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>
--- 
 arch/arm/include/asm/irq_work.h | 11 +++++++++--
 arch/arm/kernel/irq.c           |  0
 arch/arm/kernel/smp.c           |  3 +++
 drivers/irqchip/irq-gic.c       | 17 +++++++++++++----
 4 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/irq_work.h b/arch/arm/include/asm/irq_work.h
index 2dc8d7995b48..d7262a3c2f2e 100644
--- a/arch/arm/include/asm/irq_work.h
+++ b/arch/arm/include/asm/irq_work.h
@@ -1,11 +1,18 @@
 #ifndef __ASM_ARM_IRQ_WORK_H
 #define __ASM_ARM_IRQ_WORK_H
 
-#include <asm/smp_plat.h>
+extern bool irq_controller_can_ipi;
+#define irq_controller_can_ipi irq_controller_can_ipi
 
 static inline bool arch_irq_work_has_interrupt(void)
 {
-	return cpu_smp();
+#ifdef CONFIG_SMP
+	/* This depends on the IRQ controller */
+	return irq_controller_can_ipi;
+#else
+	/* The kernel is not built to support IPIs */
+	return false;
+#endif
 }
 
 #endif /* _ASM_ARM_IRQ_WORK_H */
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 7dd14e8395e6..1fa9412cc4aa 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -473,6 +473,9 @@ void __init set_smp_cross_call(void (*fn)(const struct cpumask *, unsigned int))
 		__smp_cross_call = fn;
 }
 
+/* This indicates whether the IRQ controller can IPI (including self-IPI) */
+bool irq_controller_can_ipi;
+
 static const char *ipi_types[NR_IPI] __tracepoint_string = {
 #define S(x,s)	[x] = s
 	S(IPI_WAKEUP, "CPU wakeup interrupts"),
diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index d6c404b3584d..abe8d5807c0f 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -1187,9 +1187,6 @@ static int __init __gic_init_bases(struct gic_chip_data *gic,
 		 */
 		for (i = 0; i < NR_GIC_CPU_IF; i++)
 			gic_cpu_map[i] = 0xff;
-#ifdef CONFIG_SMP
-		set_smp_cross_call(gic_raise_softirq);
-#endif
 		cpuhp_setup_state_nocalls(CPUHP_AP_IRQ_GIC_STARTING,
 					  "AP_IRQ_GIC_STARTING",
 					  gic_starting_cpu, NULL);
@@ -1207,8 +1204,20 @@ static int __init __gic_init_bases(struct gic_chip_data *gic,
 	}
 
 	ret = gic_init_bases(gic, irq_start, handle);
-	if (ret)
+	if (ret) {
 		kfree(name);
+		return ret;
+	}
+
+	if (gic == &gic_data[0]) {
+#ifdef CONFIG_SMP
+		set_smp_cross_call(gic_raise_softirq);
+#ifdef irq_controller_can_ipi
+		if (nr_cpu_ids == 1 || hweight8(gic_cpu_map[0]) == 1)
+			irq_controller_can_ipi = true;
+#endif
+#endif
+	}
 
 	return ret;
 }

-- 
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