[PATCH] MIPS: Fix broken malta qemu

From: Qais Yousef
Date: Thu Mar 17 2016 - 17:08:53 EST

Malta defconfig compiles with GIC on. Hence when compiling for SMP it causes the
new IPI code to be activated. But on qemu malta there's no GIC causing a
BUG_ON(!ipidomain) to be hit in mips_smp_ipi_init().

Since in that configuration one can only run a single core SMP (!), skip IPI
initialisation if we detect that this is the case. It is a sensible behaviour
to introduce and should keep such possible configuration to run rather than die
hard unnecessarily.

Signed-off-by: Qais Yousef <qsyousef@xxxxxxxxx>
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
arch/mips/kernel/smp.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 37708d9..27cb638 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -243,6 +243,18 @@ static int __init mips_smp_ipi_init(void)
struct irq_domain *ipidomain;
struct device_node *node;

+ /*
+ * In some cases like qemu-malta, it is desired to try SMP with
+ * a single core. Qemu-malta has no GIC, so an attempt to set any IPIs
+ * would cause a BUG_ON() to be triggered since there's no ipidomain.
+ *
+ * Since for a single core system IPIs aren't required really, skip the
+ * initialisation which should generally keep any such configurations
+ * happy and only fail hard when trying to truely run SMP.
+ */
+ if (cpumask_weight(cpu_possible_mask) == 1)
+ return 0;
node = of_irq_find_parent(of_root);
ipidomain = irq_find_matching_host(node, DOMAIN_BUS_IPI);