Messages in this thread | | | Date | Wed, 18 Aug 2021 17:58:21 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH] irqchip/gic: Convert to handle_strict_flow_irq() |
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On Tue, 17 Aug 2021 01:30:43 +0100, Valentin Schneider <valentin.schneider@arm.com> wrote: > > On 15/08/21 07:54, Marc Zyngier wrote: > > This is going and-up in a wack-a-mole game. There is probably a bunch > > of these all over the place. I'd rather squash it at the root, > > i.e. with something like this (untested): > > > > diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c > > index 099bc7e13d1b..601ad3fc47cd 100644 > > --- a/kernel/irq/chip.c > > +++ b/kernel/irq/chip.c > > @@ -410,7 +410,12 @@ void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu) > > > > void ack_irq(struct irq_desc *desc) > > { > > - desc->irq_data.chip->irq_ack(&desc->irq_data); > > + struct irq_data *data = &desc->irq_data; > > + > > + while (!data->chip->irq_ack) > > + data = data->parent_data; > > + > > + data->chip->irq_ack(&desc->irq_data); > > > > if (desc->irq_data.chip->flags & IRQCHIP_AUTOMASKS_FLOW) > > irq_state_set_flow_masked(desc); > > > > We probably need something similar for irq_eoi(). > > > > This however shows a more fundamental problem, I'm afraid. We set > > IRQCHIP_AUTOMASKS_FLOW in the GIC drivers (i.e. at the root), but test > > for it at the top of the hierarchy. As soon as we have more than a > > single layer of irqchip, this will do the wrong thing (or at least > > miss the masking optimisation). > > > > Yup. > > > This probably advocates for moving the flag into the descriptor. This > > really makes sense, as the flow is global to the whole stack, not just > > to the localised irqchip. > > > > Are we guaranteed to have > > .irq_ack \in {NULL, irq_chip_ack_parent} > > for all intermediate (!root) irqchips? I don't see why that wouldn't > be the case, and with that in mind what you described makes sense to > me.
An intermediate layer is allowed to implement its own irq_ack that is not irq_chip_ack_parent, but it then has to call irq_chip_ack_parent itself.
There is the bizarre case of drivers/gpio/gpio-thunderx.c that changes the irqchip flow to use either handle_fasteoi_ack_irq or handle_fasteoi_mask_irq, which won't play very nicely with this. Someone said Cavium?
> > > In order to restore -next into a working state, I'm temporarily > > dropping this series. Hopefully, we can sort this out before the merge > > window and reinstate it. > > > > I'm away from any keyboard for most of this week, but I'll get to it by the > weekend.
No worries, enjoy your break!
M.
-- Without deviation from the norm, progress is not possible.
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