Re: [PATCH v3] of/irq: Use interrupts-extended to find parent

[Rob Herring <robh@kernel.org>]

On Tue, 12 Apr 2022 00:15:28 -0500, Samuel Holland wrote:
> The RISC-V PLIC binding uses interrupts-extended to specify its parent
> domain(s). That binding does not allow the interrupt-parent property to
> appear in the irqchip node. This prevents of_irq_init from properly
> detecting the irqchip hierarchy.
> 
> If no interrupt-parent property is present in the enclosing bus or root
> node, then desc->interrupt_parent will be NULL for both the per-CPU
> RISC-V INTC (the actual root domain) and the RISC-V PLIC. Similarly, if
> the bus or root node specifies `interrupt-parent = <&plic>`, then
> of_irq_init will hit the `desc->interrupt_parent == np` check, and again
> all parents will be NULL. So things happen to work today for some boards
> due to Makefile ordering.
> 
> However, things break when another irqchip ("foo") is stacked on top of
> the PLIC. The bus or root node will have `interrupt-parent = <&foo>`,
> since that is what all of the other peripherals need. When of_irq_init
> runs, it will try to find the PLIC's parent domain. of_irq_find_parent
> will fall back to using the interrupt-parent property of the PLIC's
> parent node (i.e. the bus or root node), and of_irq_init will see "foo"
> as the PLIC's parent domain. But this is wrong, because "foo" is
> actually the PLIC's child domain!
> 
> So of_irq_init wrongly attempts to init the stacked irqchip before the
> PLIC. This fails and breaks booting.
> 
> Fix this by using the first node referenced by interrupts-extended as
> the parent when that property is present. This allows of_irq_init to see
> the relationship between the PLIC and the per-CPU RISC-V INTC, and thus
> only the RISC-V INTC is (correctly) considered a root domain.
> 
> Signed-off-by: Samuel Holland <samuel@sholland.org>
> ---
> 
> Changes in v3:
>  - Move the check into of_irq_init. Do not touch of_irq_find_parent.
> 
> Changes in v2:
>  - Add comments noting the assumptions made here
> 
>  drivers/of/irq.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 

Applied, thanks!