linux-kernel - Re: [PATCH v3 2/2] pinctrl: stm32: Add level interrupt support to gpio irq chip

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Date:   Mon, 23 Mar 2020 19:31:57 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Marek Vasut <marex@...x.de>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] pinctrl: stm32: Add level interrupt support to
 gpio irq chip

On Mon, 23 Mar 2020 20:19:39 +0100
Marek Vasut <marex@...x.de> wrote:

> On 3/23/20 8:04 PM, Marek Vasut wrote:
> > On 2/20/20 10:17 AM, Marc Zyngier wrote:
> >> On 2020-02-20 09:04, Linus Walleij wrote:
> >>> On Wed, Feb 19, 2020 at 3:32 PM Alexandre Torgue
> >>> <alexandre.torgue@...com> wrote:
> >>>
> >>>> GPIO hardware block is directly linked to EXTI block but EXTI handles
> >>>> external interrupts only on edge. To be able to handle GPIO interrupt on
> >>>> level a "hack" is done in gpio irq chip: parent interrupt (exti irq
> >>>> chip)
> >>>> is retriggered following interrupt type and gpio line value.
> >>>>
> >>>> Signed-off-by: Alexandre Torgue <alexandre.torgue@...com>
> >>>> Tested-by: Marek Vasut <marex@...x.de>
> >>>
> >>> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> >>>
> >>> If Marc want to merge it with patch 1/2 go ahead!
> >>
> >> I'll queue the whole thing for 5.7.
> > 
> > I have a feeling this doesn't work with threaded interrupts.
> > 
> > If the interrupt handler runs in a thread context, the EOI will happen
> > almost right away (while the IRQ handler runs) and so will the code
> > handling the IRQ retriggering. But since the IRQ handler still runs and
> > didn't return yet, the retriggering doesn't cause the IRQ handler to be
> > called again once it finishes, even if the IRQ line is still asserted.
> > And that could result in some of the retriggers now happening I think.
> > Or am I doing something wrong ?
> 
> The patch below makes my usecase work, but I don't know whether it's
> correct. Basically once the threaded IRQ handler finishes and unmasks
> the IRQ, check whether the line is asserted and retrigger if so.
> 
> diff --git a/drivers/pinctrl/stm32/pinctrl-stm32.c
> b/drivers/pinctrl/stm32/pinctrl-stm32.c
> index 9ac9ecfc2f34..060dbcb7ae72 100644
> --- a/drivers/pinctrl/stm32/pinctrl-stm32.c
> +++ b/drivers/pinctrl/stm32/pinctrl-stm32.c
> @@ -371,12 +371,26 @@ static void
> stm32_gpio_irq_release_resources(struct irq_data *irq_data)
>         gpiochip_unlock_as_irq(&bank->gpio_chip, irq_data->hwirq);
>  }
> 
> +static void stm32_gpio_irq_unmask(struct irq_data *d)
> +{
> +       struct stm32_gpio_bank *bank = d->domain->host_data;
> +       int level;
> +
> +       irq_chip_unmask_parent(d);
> +
> +       /* If level interrupt type then retrig */
> +       level = stm32_gpio_get(&bank->gpio_chip, d->hwirq);
> +       if ((level == 0 && bank->irq_type[d->hwirq] ==
> IRQ_TYPE_LEVEL_LOW) ||
> +           (level == 1 && bank->irq_type[d->hwirq] == IRQ_TYPE_LEVEL_HIGH))
> +               irq_chip_retrigger_hierarchy(d);
> +}
> +
>  static struct irq_chip stm32_gpio_irq_chip = {
>         .name           = "stm32gpio",
>         .irq_eoi        = stm32_gpio_irq_eoi,
>         .irq_ack        = irq_chip_ack_parent,
>         .irq_mask       = irq_chip_mask_parent,
> -       .irq_unmask     = irq_chip_unmask_parent,
> +       .irq_unmask     = stm32_gpio_irq_unmask,
>         .irq_set_type   = stm32_gpio_set_type,
>         .irq_set_wake   = irq_chip_set_wake_parent,
>         .irq_request_resources = stm32_gpio_irq_request_resources,
> 

OK, I see your problem now.

The usual flow is along the line of Ack+Eoi, and that's what the
current code guarantees.

Threaded interrupts do Ack+Mask+Eoi, followed by an Unmask once the
thread finishes. This unmask needs to do the retrigger as well, as you
found out.

Can you please refactor the above so that we have the common code
between unmask and eoi in a separate function, send a proper patch, and
I'll apply it on top of the current irq/irqchip-5.7 branch.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...