The Devicetree Specification states:

    The root of the interrupt tree is determined when traversal of the
    interrupt tree reaches an interrupt controller node without an
    interrupts property and thus no explicit interrupt parent.

However, of_irq_init() gratuitously assumes that a node without
interrupts has an actual interrupt parent if it finds an
interrupt-parent property higher up in the device tree.  Hence when such
a property is present (e.g. in the root node), the root interrupt
controller may not be detected as such, causing a panic:

    OF: of_irq_init: children remain, but no parents
    Kernel panic - not syncing: No interrupt controller found.

Commit e91033621d56e055 ("of/irq: Use interrupts-extended to find
parent") already fixed a first part, by checking for the presence of an
interrupts-extended property.  Fix the second part by only calling
of_irq_find_parent() when an interrupts property is present.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/of/irq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index c29f0bef7798ec02..f155054e297c989a 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -663,7 +663,7 @@ void __init of_irq_init(const struct of_device_id *matches)
 		 * are the same distance away from the root irq controller.
 		 */
 		desc->interrupt_parent = of_parse_phandle(np, "interrupts-extended", 0);
-		if (!desc->interrupt_parent)
+		if (!desc->interrupt_parent && of_property_present(np, "interrupts"))
 			desc->interrupt_parent = of_irq_find_parent(np);
 		if (desc->interrupt_parent == np) {
 			of_node_put(desc->interrupt_parent);
-- 
2.43.0

On Fri, Oct 3, 2025 at 5:08 AM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
>
> The Devicetree Specification states:
>
>     The root of the interrupt tree is determined when traversal of the
>     interrupt tree reaches an interrupt controller node without an
>     interrupts property and thus no explicit interrupt parent.
>
> However, of_irq_init() gratuitously assumes that a node without
> interrupts has an actual interrupt parent if it finds an
> interrupt-parent property higher up in the device tree.  Hence when such
> a property is present (e.g. in the root node), the root interrupt
> controller may not be detected as such, causing a panic:
>
>     OF: of_irq_init: children remain, but no parents
>     Kernel panic - not syncing: No interrupt controller found.
>
> Commit e91033621d56e055 ("of/irq: Use interrupts-extended to find
> parent") already fixed a first part, by checking for the presence of an
> interrupts-extended property.  Fix the second part by only calling
> of_irq_find_parent() when an interrupts property is present.

Seems reasonable. Why the RFC tag?

Normally I'd worry about some ancient PPC or Sparc system, but they
don't use of_irq_init().

Rob

Hi Rob,

On Fri, 3 Oct 2025 at 15:33, Rob Herring <robh@kernel.org> wrote:
> On Fri, Oct 3, 2025 at 5:08 AM Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
> > The Devicetree Specification states:
> >
> >     The root of the interrupt tree is determined when traversal of the
> >     interrupt tree reaches an interrupt controller node without an
> >     interrupts property and thus no explicit interrupt parent.
> >
> > However, of_irq_init() gratuitously assumes that a node without
> > interrupts has an actual interrupt parent if it finds an
> > interrupt-parent property higher up in the device tree.  Hence when such
> > a property is present (e.g. in the root node), the root interrupt
> > controller may not be detected as such, causing a panic:
> >
> >     OF: of_irq_init: children remain, but no parents
> >     Kernel panic - not syncing: No interrupt controller found.
> >
> > Commit e91033621d56e055 ("of/irq: Use interrupts-extended to find
> > parent") already fixed a first part, by checking for the presence of an
> > interrupts-extended property.  Fix the second part by only calling
> > of_irq_find_parent() when an interrupts property is present.
>
> Seems reasonable. Why the RFC tag?

Perhaps you might object to putting interrupt-parent in the root node
if it does not point to the root interrupt controller, or if it does
not help to simplify interrupts-extended to interrupts (like e.g. for
ARM arch timer)?

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds