powerpc/mpic: Add in-core support for cascaded MPICs

The Cell and PowerMac platforms use virtually identical cascaded-IRQ
setup code, so just merge it into the core.  Ideally this code would
trigger automatically when an MPIC device-node specifies an "interrupts"
property, perhaps even enabling MPIC_SECONDARY along the way.

Unfortunately, Benjamin Herrenschmidt has had bad experiences in the
past with the quality of Apple PowerMac device-trees, so to be safe we
will only try to parse out an IRQ if the MPIC_SECONDARY flag is set by
the caller.

Signed-off-by: Kyle Moffett <Kyle.D.Moffett@boeing.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 28 insertions, 2 deletions

diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
index 76110608543a..4e9ccb1015de 100644
--- a/arch/powerpc/sysdev/mpic.c
+++ b/arch/powerpc/sysdev/mpic.c
@@ -1111,6 +1111,22 @@ static int mpic_host_xlate(struct irq_host *h, struct device_node *ct,
         return 0;
 }
 
+/* IRQ handler for a secondary MPIC cascaded from another IRQ controller */
+static void mpic_cascade(unsigned int irq, struct irq_desc *desc)
+{
+        struct irq_chip *chip = irq_desc_get_chip(desc);
+        struct mpic *mpic = irq_desc_get_handler_data(desc);
+        unsigned int virq;
+
+        BUG_ON(!(mpic->flags & MPIC_SECONDARY));
+
+        virq = mpic_get_one_irq(mpic);
+        if (virq != NO_IRQ)
+                generic_handle_irq(virq);
+
+        chip->irq_eoi(&desc->irq_data);
+}
+
 static struct irq_host_ops mpic_host_ops = {
         .match = mpic_host_match,
         .map = mpic_host_map,
@@ -1402,8 +1418,7 @@ void __init mpic_set_default_senses(struct mpic *mpic, u8 *senses, int count)
 
 void __init mpic_init(struct mpic *mpic)
 {
-        int i;
-        int cpu;
+        int i, cpu;
 
         BUG_ON(mpic->num_sources == 0);
 
@@ -1488,6 +1503,17 @@ void __init mpic_init(struct mpic *mpic)
                                   GFP_KERNEL);
         BUG_ON(mpic->save_data == NULL);
 #endif
+
+        /* Check if this MPIC is chained from a parent interrupt controller */
+        if (mpic->flags & MPIC_SECONDARY) {
+                int virq = irq_of_parse_and_map(mpic->node, 0);
+                if (virq != NO_IRQ) {
+                        printk(KERN_INFO "%s: hooking up to IRQ %d\n",
+                                        mpic->node->full_name, virq);
+                        irq_set_handler_data(virq, mpic);
+                        irq_set_chained_handler(virq, &mpic_cascade);
+                }
+        }
 }
 
 void __init mpic_set_clk_ratio(struct mpic *mpic, u32 clock_ratio)