xtensa: add device trees support

Device trees allow specification of hardware topology and device
parameters at runtime instead of hard-coding them in platform setup
code. This allows running single binary kernel on a range of compatible
boards.

New boot parameters tag BP_TAG_FDT is allocated and a pointer to flat
device tree is passed in it.

Note that current interrupt mapping scheme uses single cell for
interrupt identification. That means that IRQ numbers used in DTS must
be CPU internal IRQ numbers, not external. It is possible to extend
interrupt identification to two cells, and use second cell to tell
external IRQ numbers form internal. That would allow to use single DTS
on multiple boards with different mapping of external IRQ numbers.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/xtensa/kernel/irq.c b/arch/xtensa/kernel/irq.c
index e90d782..6f4f974 100644
--- a/arch/xtensa/kernel/irq.c
+++ b/arch/xtensa/kernel/irq.c
@@ -19,6 +19,7 @@
 #include <linux/irq.h>
 #include <linux/kernel_stat.h>
 #include <linux/irqdomain.h>
+#include <linux/of.h>
 
 #include <asm/uaccess.h>
 #include <asm/platform.h>
@@ -199,8 +200,17 @@ void __init init_IRQ(void)
 	cached_irq_mask = 0;
 	set_sr(~0, intclear);
 
+#ifdef CONFIG_OF
+	/* The interrupt controller device node is mandatory */
+	intc = of_find_compatible_node(NULL, NULL, "xtensa,pic");
+	BUG_ON(!intc);
+
+	root_domain = irq_domain_add_linear(intc, NR_IRQS,
+			&xtensa_irq_domain_ops, NULL);
+#else
 	root_domain = irq_domain_add_legacy(intc, NR_IRQS, 0, 0,
 			&xtensa_irq_domain_ops, NULL);
+#endif
 	irq_set_default_host(root_domain);
 
 	variant_init_irq();