linux-kernel - Re: [PATCH v4 3/4] pinctrl: qcom: Don't clear pending interrupts when enabling

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Message-ID: <160818088793.1580929.1672018770454181938@swboyd.mtv.corp.google.com>
Date:   Wed, 16 Dec 2020 20:54:47 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Jason Cooper <jason@...edaemon.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Maulik Shah <mkshah@...eaurora.org>,
        linux-arm-msm@...r.kernel.org,
        Srinivas Ramana <sramana@...eaurora.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        linux-gpio@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/4] pinctrl: qcom: Don't clear pending interrupts when enabling

Quoting Douglas Anderson (2020-12-11 14:15:37)
> In Linux, if a driver does disable_irq() and later does enable_irq()
> on its interrupt, I believe it's expecting these properties:
> * If an interrupt was pending when the driver disabled then it will
>   still be pending after the driver re-enables.
> * If an edge-triggered interrupt comes in while an interrupt is
>   disabled it should assert when the interrupt is re-enabled.
> 
> If you think that the above sounds a lot like the disable_irq() and
> enable_irq() are supposed to be masking/unmasking the interrupt
> instead of disabling/enabling it then you've made an astute
> observation.  Specifically when talking about interrupts, "mask"
> usually means to stop posting interrupts but keep tracking them and
> "disable" means to fully shut off interrupt detection.  It's
> unfortunate that this is so confusing, but presumably this is all the
> way it is for historical reasons.
> 
> Perhaps more confusing than the above is that, even though clients of
> IRQs themselves don't have a way to request mask/unmask
> vs. disable/enable calls, IRQ chips themselves can implement both.
> ...and yet more confusing is that if an IRQ chip implements
> disable/enable then they will be called when a client driver calls
> disable_irq() / enable_irq().
> 
> It does feel like some of the above could be cleared up.  However,
> without any other core interrupt changes it should be clear that when
> an IRQ chip gets a request to "disable" an IRQ that it has to treat it
> like a mask of that IRQ.
> 
> In any case, after that long interlude you can see that the "unmask
> and clear" can break things.  Maulik tried to fix it so that we no
> longer did "unmask and clear" in commit 71266d9d3936 ("pinctrl: qcom:
> Move clearing pending IRQ to .irq_request_resources callback"), but it
> only handled the PDC case (it also had problems, but that's the
> subject of another patch).  Let's fix this for the non-PDC case.
> 
> From my understanding the source of the phantom interrupt in the
> non-PDC case was the one that could have been introduced in
> msm_gpio_irq_set_type().  Let's handle that one and then get rid of
> the clear.
> 
> Fixes: 4b7618fdc7e6 ("pinctrl: qcom: Add irq_enable callback for msm gpio")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@...omium.org>

One comment clarification below.

> I don't have lots of good test cases here, so hopefully someone from
> Qualcomm can confirm that this works well for them and there isn't
> some other phantom interrupt source that I'm not aware of.
> 
> Changes in v4:
> - ("pinctrl: qcom: Don't clear pending interrupts when enabling") split for v4.
> 
>  drivers/pinctrl/qcom/pinctrl-msm.c | 32 +++++++++++++-----------------
>  1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/pinctrl/qcom/pinctrl-msm.c b/drivers/pinctrl/qcom/pinctrl-msm.c
> index 588df91274e2..f785646d1df7 100644
> --- a/drivers/pinctrl/qcom/pinctrl-msm.c
> +++ b/drivers/pinctrl/qcom/pinctrl-msm.c
> @@ -1046,6 +1032,16 @@ static int msm_gpio_irq_set_type(struct irq_data *d, unsigned int type)
>         }
>         msm_writel_intr_cfg(val, pctrl, g);
>  
> +       /*
> +        * The first time we set RAW_STATUS_EN it could trigger an interrupt.
> +        * Clear it.  This is safe because we have IRQCHIP_SET_TYPE_MASKED.

Clear the interrupt? 'it' is ambiguous.

> +        */
> +       if (!was_enabled) {
> +               val = msm_readl_intr_status(pctrl, g);
> +               val &= ~BIT(g->intr_status_bit);
> +               msm_writel_intr_status(val, pctrl, g);
> +       }
> +
>         if (test_bit(d->hwirq, pctrl->dual_edge_irqs))
>                 msm_gpio_update_dual_edge_pos(pctrl, g, d);
>