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    SubjectRe: [PATCH 6/9] gpio: Add support for hierarchical IRQ domains
    Hi Thierry!

    Thanks for the patch!

    I am a bit ignorant about irqdomains so I will probably need an ACK
    from some irq maintainer before I can apply this.

    On Fri, Sep 21, 2018 at 12:25 PM Thierry Reding
    <thierry.reding@gmail.com> wrote:

    > From: Thierry Reding <treding@nvidia.com>
    >
    > Hierarchical IRQ domains can be used to stack different IRQ controllers
    > on top of each other. One specific use-case where this can be useful is
    > if a power management controller has top-level controls for wakeup
    > interrupts. In such cases, the power management controller can be a
    > parent to other interrupt controllers and program additional registers
    > when an IRQ has its wake capability enabled or disabled.
    >
    > Signed-off-by: Thierry Reding <treding@nvidia.com>

    While I think it is really important that we start supporting hierarchical
    irqdomains in the gpiolib core, I want a more complete approach,
    so that drivers that need hierarchical handling of irqdomains
    can get the same support from gpiolib as they get for simple
    domains.

    > @@ -1918,7 +1918,9 @@ static int gpiochip_add_irqchip(struct gpio_chip *gpiochip,
    > type = IRQ_TYPE_NONE;
    > }
    >
    > - gpiochip->to_irq = gpiochip_to_irq;
    > + if (!gpiochip->to_irq)
    > + gpiochip->to_irq = gpiochip_to_irq;

    So here you let the drivers override the .to_irq() function and that
    I think gets confusing as we are asking gpiolib to handle our
    irqchip.


    > - gpiochip->irq.domain = irq_domain_add_simple(np, gpiochip->ngpio,
    > - gpiochip->irq.first,
    > - ops, gpiochip);
    > + if (gpiochip->irq.parent_domain)
    > + gpiochip->irq.domain = irq_domain_add_hierarchy(gpiochip->irq.parent_domain,
    > + 0, gpiochip->ngpio,
    > + np, ops, gpiochip);
    > + else
    > + gpiochip->irq.domain = irq_domain_add_simple(np, gpiochip->ngpio,
    > + gpiochip->irq.first,
    > + ops, gpiochip);

    So this part is great: if we pass in a parent domain the core helps us
    create the hierarchy.

    But the stuff in .to_irq() should also be handled in the gpiolib core:
    the irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, &spec) for
    example. That way you should not need any external .to_irq() function.

    I can't see if you need to pull more stuff into the core to accomplish
    that, but I think in essence the core gpiolib needs to be more helpful
    with hierarchies.

    Yours,
    Linus Walleij

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