[PATCH 1/1] irqchip: irq-gic: forward SGI to itself for cortex-a7 single core

[Peter Chen]

According to Cortex-A7 MPCore TRM, ch8.3.1, Distributor register summary,
GICD_ITARGETSRn:

	The register that contains the SGI and PPI interrupts is
       	read-only and the value is implementation defined. For
       	Cortex-A7 configurations with only one processor, these
       	registers are RAZ/WI.

So, the GICD_ITARGETSR[0..7] is read-only, and the value is 0 for
cortex-a7 single core platform if the SoC is cortex-a7 mpcore version.
So the cupmask from gic_get_cpumask is 0.

At ARM Generic Interrupt Controller Architecture version 2.0,
ch4.3.15 Software Generated Interrupt Register, GICD_SGIR,
The distributor will process the requested SGI according to
register TargetListFilter and CPUTargetList. At current gic code,
it takes TargetListFilter as 0b00, and forward the interrupt to
cpumask (variable map at gic_raise_softirq) getting from gic_get_cpumask.
but cpumask is 0 according to above explanation for cortex-a7 single core
platform, so, both TargetListFilter and CPUTargetList are 0, and the
distributor does not forward the interrupt to any CPU interface according
to gic documentation, then the SGI can't be occurred.

We have found this problem at nxp imx6ul platform, which is a cortex-a7
single core platform, the irq work (triggered by SGI at ARM) can't be
occurred which is needed for cpufreq, then the system has failed to boot
and reboot [1].

In this commit, we set TargetListFilter as 0b10 to fix this problem, it
forwards the interrupt only to CPU0 and only cortex-a7 single core platform
uses this setting currently.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-May/
    430545.html

Cc: Russell King <linux at armlinux.org.uk>
Cc: Shawn Guo <shawnguo at kernel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Cc: Jason Liu <jason.hui.liu at nxp.com>
Cc: Anson Huang <anson.huang at nxp.com>
Cc: Frank Li <frank.li at nxp.com>
Cc: Fabio Estevam <fabio.estevam at nxp.com>
Cc: Ping Bai <ping.bai at nxp.com>

Signed-off-by: Peter Chen <peter.chen at nxp.com>
---
 drivers/irqchip/irq-gic.c | 39 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index c2cab57..625ae6d 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -764,6 +764,23 @@ static int gic_pm_init(struct gic_chip_data *gic)
 #endif
 
 #ifdef CONFIG_SMP
+static void gic_raise_softirq_itself(const struct cpumask *mask,
+				     unsigned int irq)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&irq_controller_lock, flags);
+
+	/*
+	 * Forward the interrupt only to the CPU interface of the processor
+	 * that requested the interrupt.
+	 */
+	writel_relaxed(0x2000000 | irq, gic_data_dist_base(&gic_data[0])
+					+ GIC_DIST_SOFTINT);
+
+	raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
+}
+
 static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
 {
 	int cpu;
@@ -1162,9 +1179,6 @@ 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);
@@ -1336,6 +1350,16 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
 	gic_set_kvm_info(&gic_v2_kvm_info);
 }
 
+static bool __init gic_is_a7_singlecore(struct gic_chip_data *gic,
+					struct device_node *node)
+{
+	if (!of_device_is_compatible(node, "arm,cortex-a7-gic"))
+		return false;
+
+	return !(readl_relaxed(gic_data_dist_base(gic) + GIC_DIST_CTR) & 0xe0);
+
+}
+
 int __init
 gic_of_init(struct device_node *node, struct device_node *parent)
 {
@@ -1367,6 +1391,15 @@ gic_of_init(struct device_node *node, struct device_node *parent)
 		return ret;
 	}
 
+	if (gic == &gic_data[0]) {
+#ifdef CONFIG_SMP
+		if (gic_is_a7_singlecore(gic, node))
+			set_smp_cross_call(gic_raise_softirq_itself);
+		else
+			set_smp_cross_call(gic_raise_softirq);
+#endif
+	}
+
 	if (!gic_cnt) {
 		gic_init_physaddr(node);
 		gic_of_setup_kvm_info(node);
-- 
1.9.1