Hi Rob!
On Tue, 2025-03-11 at 12:55 -0500, Rob Herring wrote:
> > An #interrupt-cells = <0> property may arguably be a right answer for an
> > interrupt controller having just one interrupt and no options to configure.
> > There are anyway already existing examples in the tree, both in DTs and in
> > the bindings.
>
> The existing examples are broken and hacks to take advantage of Linux
> implementation details (IRQCHIP_DECLARE()).
>
> And #interrupt-cells==0 can't work with 'interrupts'.
I agree.
> > Now the problem is that of_irq_count() called on an interrupt generating
> > device having one of the former controllers as parent would result in an
> > endless loop. It's especially unpleasant in the startup where
> > of_irq_count() <= ... <= of_platform_default_populate_init() will silently
> > hang forever (unless a watchdog bites).
> >
> > Prevent others from spending the same time on debugging this by refusing to
> > parse more than one IRQ for such controllers.
>
> I'll happily take a dtschema patch to warn on 0 cells. Then you can find
> the problem at build time. I generally don't think it's the kernel's job
> to validate a DT, but if the code can handle something like this then
> that's good.
>
> >
> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> > ---
> > drivers/of/irq.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/of/irq.c b/drivers/of/irq.c
> > index 6c843d54ebb11..b3a359c7641d3 100644
> > --- a/drivers/of/irq.c
> > +++ b/drivers/of/irq.c
> > @@ -381,6 +381,13 @@ int of_irq_parse_one(struct device_node *device, int index, struct of_phandle_ar
> > goto out;
> > }
> >
> > + if (!intsize && index) {
>
> Why are you checking index?
This way of_irq_count() gives "1" on the corresponding nodes.
Do you think that returning "-EINVAL" "if (!intsize)" would
make more sense? I'm concerned about this place because the
code doesn't even crash, but rather hangs until watchdog comes,
which means, there is no backtrace, nothing.
> > + pr_debug("%pOF trying to map IRQ %d in %pOF having #interrupt-cells = <0>\n",
> > + device, index, p);
> > + res = -EINVAL;
> > + goto out;
> > + }
> > +
> > pr_debug(" parent=%pOF, intsize=%d\n", p, intsize);
> >
> > /* Copy intspec into irq structure */
--
Alexander Sverdlin
Siemens AG
www.siemens.com
