linux-kernel - Re: [PATCH 2/2] gpio/rockchip: Toggle edge trigger mode after acking

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Date:   Fri, 26 Aug 2022 10:54:08 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Chen Jeffy <jeffy.chen@...k-chips.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        Heiko Stuebner <heiko@...ech.de>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH 2/2] gpio/rockchip: Toggle edge trigger mode after acking

On Tue, Aug 23, 2022 at 4:50 AM Chen Jeffy <jeffy.chen@...k-chips.com> wrote:

> The thing is, we are currently toggling the trigger mode to make sure it
> matches the current GPIO level (e.g. level low -> rising edge mode),
> than ack it in gpio IRQ handler.

Yes this is an old trick, I don't know if I invented it again for Linux in
commit cc890cd78acd7ab03442907d354b6af34e973cb3
in 2011, surely the trick must be well known.

Back then I did it like this:

+       val = readl(U300_PIN_REG(offset, icr));
+       /* Set mode depending on state */
+       if (u300_gpio_get(&gpio->chip, offset)) {
+               /* High now, let's trigger on falling edge next then */
+               writel(val & ~U300_PIN_BIT(offset), U300_PIN_REG(offset, icr));
+               dev_dbg(gpio->dev, "next IRQ on falling edge on pin %d\n",
+                       offset);
+       } else {
+               /* Low now, let's trigger on rising edge next then */
+               writel(val | U300_PIN_BIT(offset), U300_PIN_REG(offset, icr));
+               dev_dbg(gpio->dev, "next IRQ on rising edge on pin %d\n",
+                       offset);
+       }

Notice that I read the current level of the raw input to decide what the next
trigger should be. The Rockchip driver does not do this, maybe that works
better?

Yours,
Linus Walleij