linux-kernel - [PATCH 2/4] irqchip/gic: Allow self-SGIs for SMP on UP configurations

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Date:   Mon, 22 Aug 2016 09:23:38 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Fabio Estevam <fabio.estevam@....com>,
        John Stultz <john.stultz@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Jason Cooper <jason@...edaemon.net>,
        David Daney <david.daney@...ium.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/4] irqchip/gic: Allow self-SGIs for SMP on UP configurations

On systems where a single CPU is present, the GIC may not support
having SGIs delivered to a target list. In that case, we use the
self-SGI mechanism to allow the interrupt to be delivered locally.

Tested-by: Fabio Estevam <fabio.estevam@....com>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 drivers/irqchip/irq-gic.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index c2cab57..390fac5 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -769,6 +769,13 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
 	int cpu;
 	unsigned long flags, map = 0;
 
+	if (unlikely(nr_cpu_ids == 1)) {
+		/* Only one CPU? let's do a self-IPI... */
+		writel_relaxed(2 << 24 | irq,
+			       gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
+		return;
+	}
+
 	raw_spin_lock_irqsave(&irq_controller_lock, flags);
 
 	/* Convert our logical CPU mask into a physical one. */
-- 
2.1.4