Date:   Mon, 21 Dec 2020 21:30:38 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org,
        Srinivas Ramana <sramana@...eaurora.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        linux-gpio@...r.kernel.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

Hi Doug,

On 12/12/2020 3:45 AM, Douglas Anderson wrote:
> 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>
> ---
> 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
> @@ -774,7 +774,7 @@ static void msm_gpio_irq_mask(struct irq_data *d)
>   	raw_spin_unlock_irqrestore(&pctrl->lock, flags);
>   }
>   
> -static void msm_gpio_irq_clear_unmask(struct irq_data *d, bool status_clear)
> +static void msm_gpio_irq_unmask(struct irq_data *d)
>   {
>   	struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
>   	struct msm_pinctrl *pctrl = gpiochip_get_data(gc);
> @@ -792,17 +792,6 @@ static void msm_gpio_irq_clear_unmask(struct irq_data *d, bool status_clear)
>   
>   	raw_spin_lock_irqsave(&pctrl->lock, flags);
>   
> -	if (status_clear) {
> -		/*
> -		 * clear the interrupt status bit before unmask to avoid
> -		 * any erroneous interrupts that would have got latched
> -		 * when the interrupt is not in use.
> -		 */
> -		val = msm_readl_intr_status(pctrl, g);
> -		val &= ~BIT(g->intr_status_bit);
> -		msm_writel_intr_status(val, pctrl, g);
> -	}
> -
Removing above does not cover the case where GPIO IRQ do not have parent 
PDC.

Specifically, for edge IRQs during masking we donot clear 
intr_raw_status_bit.
see below at msm_gpio_irq_mask()

         if (irqd_get_trigger_type(d) & IRQ_TYPE_LEVEL_MASK)
                 val &= ~BIT(g->intr_raw_status_bit);

we have to keep the bit set anyway so that edges are latched while the 
line is masked.

The problem is even when GPIO is set to some other function like 
"mi2s_2" it can still sense the line at make
interrupt pending depending on the line toggle if intr_raw_status_bit is 
left set.

I have thought of solution to this,

1) During msm_gpio_irq_mask() we keep intr_raw_status_bit set already in 
today's code
This will make edges to latch when the line is masked.
so no change required for this.

2) During msm_pinmux_set_mux() if we set GPIO to anyother function than 
GPIO interrupt mode,
we clear intr_raw_status_bit, so the interrupt cannot latch when GPIO is 
used in other function.
Below snippet can be inserted in msm_pinmux_set_mux()

         val |= i << g->mux_bit;
         msm_writel_ctl(val, pctrl, g);

+        if (i != gpio_func) {
+                val = msm_readl_intr_cfg(pctrl, g);
+                val &= ~BIT(g->intr_raw_status_bit);
+                msm_writel_intr_cfg(val, pctrl, g);
+        }
+
         raw_spin_unlock_irqrestore(&pctrl->lock, flags);

3) During msm_gpio_irq_unmask(), if the intr_raw_status_bit is not set, 
then clear the pending IRQ.
specifically setting this bit itself can cause the error IRQ, so clear 
it when setting this.

for edge IRQ, intr_raw_status_bit can only be cleared in 
msm_pinmux_set_mux() so clearing pending
IRQ should not loose any edges since we know GPIO was used in other 
function mode like mi2s_2 for
which we do not need to latch IRQs.
Below snippet can be inserted in msm_gpio_irq_unmask()

+       was_enabled = val & BIT(g->intr_raw_status_bit);
         val |= BIT(g->intr_raw_status_bit);
         val |= BIT(g->intr_enable_bit);
         msm_writel_intr_cfg(val, pctrl, g);

+       if (!was_enabled) {
+               val = msm_readl_intr_status(pctrl, g);
+               val &= ~BIT(g->intr_status_bit);
+               msm_writel_intr_status(val, pctrl, g);
+       }
+
         set_bit(d->hwirq, pctrl->enabled_irqs);

This can cover the cases for which the GPIO do not have parent.

Thanks,
Maulik

>   	val = msm_readl_intr_cfg(pctrl, g);
>   	val |= BIT(g->intr_raw_status_bit);
>   	val |= BIT(g->intr_enable_bit);
> @@ -822,7 +811,7 @@ static void msm_gpio_irq_enable(struct irq_data *d)
>   		irq_chip_enable_parent(d);
>   
>   	if (!test_bit(d->hwirq, pctrl->skip_wake_irqs))
> -		msm_gpio_irq_clear_unmask(d, true);
> +		msm_gpio_irq_unmask(d);
>   }
>   
>   static void msm_gpio_irq_disable(struct irq_data *d)
> @@ -837,11 +826,6 @@ static void msm_gpio_irq_disable(struct irq_data *d)
>   		msm_gpio_irq_mask(d);
>   }
>   
> -static void msm_gpio_irq_unmask(struct irq_data *d)
> -{
> -	msm_gpio_irq_clear_unmask(d, false);
> -}
> -
>   /**
>    * msm_gpio_update_dual_edge_parent() - Prime next edge for IRQs handled by parent.
>    * @d: The irq dta.
> @@ -936,6 +920,7 @@ static int msm_gpio_irq_set_type(struct irq_data *d, unsigned int type)
>   	struct msm_pinctrl *pctrl = gpiochip_get_data(gc);
>   	const struct msm_pingroup *g;
>   	unsigned long flags;
> +	bool was_enabled;
>   	u32 val;
>   
>   	if (msm_gpio_needs_dual_edge_parent_workaround(d, type)) {
> @@ -997,6 +982,7 @@ static int msm_gpio_irq_set_type(struct irq_data *d, unsigned int type)
>   	 * could cause the INTR_STATUS to be set for EDGE interrupts.
>   	 */
>   	val = msm_readl_intr_cfg(pctrl, g);
> +	was_enabled = val & BIT(g->intr_raw_status_bit);
>   	val |= BIT(g->intr_raw_status_bit);
>   	if (g->intr_detection_width == 2) {
>   		val &= ~(3 << g->intr_detection_bit);
> @@ -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.
> +	 */
> +	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);
>   

-- 
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