linux-kernel - Re: 0001-add-amlogic-gpio-to-irq

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Date:   Fri, 04 Dec 2020 15:24:09 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        林圣欢 <linshenghuan@...gtu-china.com>
Cc:     khilman <khilman@...libre.com>,
        narmstrong <narmstrong@...libre.com>,
        "martin.blumenstingl" <martin.blumenstingl@...glemail.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic <linux-amlogic@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 0001-add-amlogic-gpio-to-irq

On Fri 04 Dec 2020 at 10:13, Linus Walleij <linus.walleij@...aro.org> wrote:

> Hi Lisheng,
>
> this patch got a bit mangled but I get where you're going.
>
> I think Meson needs to be augmented to use hierarchical gpiolib irqchip
> because this seems to be what the system is doing.
>
> So start with drivers/pinctrl/meson/Kconfig and add:
>
> select GPIOLIB_IRQCHIP
> select IRQ_DOMAIN_HIEARARCHY
>
> Then use the generic hierarchical gpiolib irqchip as described
> in Documentation/driver-api/gpio/driver.rst
> Type
> git grep child_to_parent_hwirq
> for several examples of how to do this.

One reason the irqchip has not been linked to the gpio controller so far
is IRQ_EDGE_BOTH which the irqchip does not support (expect for the
latest sm1 family)

This is a problem we discussed a couple of years ago.

This HW only has 8 irqs that can each be mapped to a pin. No direct
translation can be made, we have to allocate an irq to monitor the line.
So when gpio_to_irq() was called, we had to do that allocation dynamically
to return a valid irq number. Since there was no counter part to
gpio_to_irq(), those allocation cannot be freed during the lifetime of
the device.

When drivers relying IRQ_EDGE_BOTH first try the `gpio_to_irq()`,
allocating the irq works but setting the type does not. We are then left
with unused allocated irqs (and we don't have much)

Frameworks using gpio_to_irq() are often capable() of parsing interrupt
properties directly too. So far, it was enough to work around the problem.

I admit, I have not been following gpiolib closely since then, maybe
some progress have been made

>
> Yours,
> Linus Walleij