linux-kernel - Re: [PATCH v5 2/3] gpio: loongson: add gpio driver support

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Date:   Tue, 13 Dec 2022 10:36:24 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Yinbo Zhu <zhuyinbo@...ngson.cn>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        WANG Xuerui <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Juxin Gao <gaojuxin@...ngson.cn>,
        Bibo Mao <maobibo@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
        Arnaud Patard <apatard@...driva.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Jianmin Lv <lvjianmin@...ngson.cn>,
        Hongchen Zhang <zhanghongchen@...ngson.cn>,
        Liu Peibao <liupeibao@...ngson.cn>
Subject: Re: [PATCH v5 2/3] gpio: loongson: add gpio driver support

On Mon, Dec 12, 2022 at 9:13 AM Yinbo Zhu <zhuyinbo@...ngson.cn> wrote:

> mask_irq/unmask_irq/irq_ack/ function always be called by
> handle_level_irq/handle_edge_irq in current irq domain. and the
> handle_level_irq/handle_edge_irq will be called  by handle_irq_desc that
> ask know which irq is.
>
> when a peripheral need to use a gpio irq that gpio irq driver need know
> irq status and call irq desc->irq_handler.
>
> so I don't got it about which case it is unnecessary to know which irq.

Sorry I don't understand what you are asking, can you elaborate?

Do you mean that you don't know which driver will not call ->to_irq()
on the gpiochip? That would be any driver that takes an IRQ directly in
the device tree:

gpio: gpio {
    interrupt-controller;
    #interrupt-cells = <2>;
    ....
};

device {
    interrupts = <&gpio 14 IRQ_TYPE_LEVEL_HIGH>;
    ....
};

This case will only call the irqchip callbacks and will never call
the .to_irq() on the gpio_chip.

> > You find an example of a hierarchical GPIO irqchip using the
> > GPIOLIB_IRQCHIP in drivers/gpio/gpio-ixp4xx.c.
>
> Loongson-2 gpio irq hardware only a enable register, and when a gpio irq
> happen, then will has a such flow:  "cpuintc -> liointc -> gpioinc ->
> generic_handle_domain_irq -> handle_level_irq ->
> peripheral-action(action->handler)"
>
> generic_handle_domain_irq need rely on specific hwirq that ask gpio irq
> hardware has a status register but Loongson-2 gpio irq hardware doesn't
> have it.
>
> so I still think it wasn't appropriate that for loongson-2 gpio driver
> add a irq chip.

generic_handle_domain_irq() is of no concern, what matters is if
your interrupt is hierarchical or not, the callback in the GPIO chip
can be a simple remapping of the numberspace followed by
a call to the parent callbacks.

Yours,
Linus Walleij