irqdomain: Let irq_domain_mapping display hierarchical domains

Hierarchical domains seem to be hard to grasp, and a number of
aspiring kernel hackers find them utterly discombobulating.

In order to ease their pain, let's make them appear in
/sys/kernel/debug/irq_domain_mapping, such as the following:

   96  0x81808  MSI    0x          (null) RADIX   MSI
   96+ 0x00063  GICv2m 0xffff8003ee116980 RADIX   GICv2m
   96+ 0x00063  GICv2  0xffff00000916bfd8 LINEAR  GICv2

[output compressed to fit in a commit log]

This shows that IRQ96 is implemented by a stack of three domains,
the + sign indicating the stacking.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: http://lkml.kernel.org/r/20170512115538.10767-2-marc.zyngier@arm.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/irqdomain.c

@@ -746,13 +746,54 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
 EXPORT_SYMBOL_GPL(irq_find_mapping);
 
 #ifdef CONFIG_IRQ_DOMAIN_DEBUG
+static void virq_debug_show_one(struct seq_file *m, struct irq_desc *desc)
+{
+	struct irq_domain *domain;
+	struct irq_data *data;
+
+	domain = desc->irq_data.domain;
+	data = &desc->irq_data;
+
+	while (domain) {
+		unsigned int irq = data->irq;
+		unsigned long hwirq = data->hwirq;
+		struct irq_chip *chip;
+		bool direct;
+
+		if (data == &desc->irq_data)
+			seq_printf(m, "%5d  ", irq);
+		else
+			seq_printf(m, "%5d+ ", irq);
+		seq_printf(m, "0x%05lx  ", hwirq);
+
+		chip = irq_data_get_irq_chip(data);
+		seq_printf(m, "%-15s  ", (chip && chip->name) ? chip->name : "none");
+
+		seq_printf(m, data ? "0x%p  " : "  %p  ",
+			   irq_data_get_irq_chip_data(data));
+
+		seq_printf(m, "   %c    ", (desc->action && desc->action->handler) ? '*' : ' ');
+		direct = (irq == hwirq) && (irq < domain->revmap_direct_max_irq);
+		seq_printf(m, "%6s%-8s  ",
+			   (hwirq < domain->revmap_size) ? "LINEAR" : "RADIX",
+			   direct ? "(DIRECT)" : "");
+		seq_printf(m, "%s\n", domain->name);
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+		domain = domain->parent;
+		data = data->parent_data;
+#else
+		domain = NULL;
+#endif
+	}
+}
+
 static int virq_debug_show(struct seq_file *m, void *private)
 {
 	unsigned long flags;
 	struct irq_desc *desc;
 	struct irq_domain *domain;
 	struct radix_tree_iter iter;
-	void *data, **slot;
+	void **slot;
 	int i;
 
 	seq_printf(m, " %-16s  %-6s  %-10s  %-10s  %s\n",
@@ -782,30 +823,7 @@ static int virq_debug_show(struct seq_file *m, void *private)
 			continue;
 
 		raw_spin_lock_irqsave(&desc->lock, flags);
-		domain = desc->irq_data.domain;
-
-		if (domain) {
-			struct irq_chip *chip;
-			int hwirq = desc->irq_data.hwirq;
-			bool direct;
-
-			seq_printf(m, "%5d  ", i);
-			seq_printf(m, "0x%05x  ", hwirq);
-
-			chip = irq_desc_get_chip(desc);
-			seq_printf(m, "%-15s  ", (chip && chip->name) ? chip->name : "none");
-
-			data = irq_desc_get_chip_data(desc);
-			seq_printf(m, data ? "0x%p  " : "  %p  ", data);
-
-			seq_printf(m, "   %c    ", (desc->action && desc->action->handler) ? '*' : ' ');
-			direct = (i == hwirq) && (i < domain->revmap_direct_max_irq);
-			seq_printf(m, "%6s%-8s  ",
-				   (hwirq < domain->revmap_size) ? "LINEAR" : "RADIX",
-				   direct ? "(DIRECT)" : "");
-			seq_printf(m, "%s\n", desc->irq_data.domain->name);
-		}
-
+		virq_debug_show_one(m, desc);
 		raw_spin_unlock_irqrestore(&desc->lock, flags);
 	}