Re: [PATCH] irqchip/gic: Convert to handle_strict_flow_irq()

On Sun, 22 Aug 2021 23:16:10 +0100,
Valentin Schneider [off-list ref] wrote:

On 18/08/21 17:58, Marc Zyngier wrote:

quoted

On Tue, 17 Aug 2021 01:30:43 +0100,
Valentin Schneider [off-list ref] wrote:

quoted

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.

Right, makes sense.

quoted

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?

Humph...

I'm not familiar at all with the gpiolib irqchips, but I was under the
impression those would involve chained IRQs (it does appear to be the case
for the pl061 GPIOs on a Juno). For those, the innermost desc would be handled
via chained_irq_{enter, exit}() [!!!], and the outermost one via whatever
flow was installed by the relevant driver.

Not all of them are built like this. There is actually a bunch of
these build as full hierarchies (QC, nvidia and some others).

I can't easily grok what goes on between that gpio-thunderx.c driver and
gpiolib, but since that GPIO chip has

        .irq_eoi		= irq_chip_eoi_parent,

and

        girq->parent_domain =
                irq_get_irq_data(txgpio->msix_entries[0].vector)->domain;

(GPIOs hooked to MSI-X? Do I want to know?)

It's good, isn't it? TX1 has all its HW appearing as PCI, even if it
clearly isn't PCI underneath.

I'm guessing it is *not* chained, which means the irq_set_handler_locked()
affects the entire stack :/

It does. We can probably fix that, but I won't be able to test (my TX1
was taken away a few months ago...). I'll accept body donations, for
scientific purposes.

[!!!] Speaking of chained IRQs, I'm now thinking this series breaks them;
chained_irq_enter() + chained_irq_exit() will only issue an ->irq_eoi(),
skipping the ->irq_ack()... One more thing to add to the list!

Urghh... Yeah, that's awful.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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