linux-kernel - [PATCH 1/3] pinctrl: msm: Really mask level interrupts to prevent latching

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Date:   Mon, 18 Jun 2018 13:52:53 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Doug Anderson <dianders@...omium.org>
Subject: [PATCH 1/3] pinctrl: msm: Really mask level interrupts to prevent latching

The interrupt controller hardware in this pin controller has two status
enable bits. The first "normal" status enable bit enables or disables
the summary interrupt line being raised when a gpio interrupt triggers
and the "raw" status enable bit allows or prevents the hardware from
latching an interrupt into the status register for a gpio interrupt.
Currently we just toggle the "normal" status enable bit in the mask and
unmask ops so that the summary irq interrupt going to the CPU's
interrupt controller doesn't trigger for the masked gpio interrupt.

For a level triggered interrupt, the flow would be as follows: the pin
controller sees the interrupt, latches the status into the status
register, raises the summary irq to the CPU, summary irq handler runs
and calls handle_level_irq(), handle_level_irq() masks and acks the gpio
interrupt, the interrupt handler runs, and finally unmask the interrupt.
When the interrupt handler completes, we expect that the interrupt line
level will go back to the deasserted state so the genirq code can unmask
the interrupt without it triggering again.

If we only mask the interrupt by clearing the "normal" status enable bit
then we'll ack the interrupt but it will continue to show up as pending
in the status register because the raw status bit is enabled, the
hardware hasn't deasserted the line, and thus the asserted state latches
into the status register again. When the hardware deasserts the
interrupt the pin controller still thinks there is a pending unserviced
level interrupt because it latched it earlier. This behavior causes
software to see an extra interrupt for level type interrupts each time
the interrupt is handled.

Let's fix this by clearing the raw status enable bit for level type
interrupts so that the hardware stops latching the status of the
interrupt after we ack it. We don't do this for edge type interrupts
because it seems that toggling the raw status enable bit for edge type
interrupts causes spurious edge interrupts.

Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Doug Anderson <dianders@...omium.org>
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/pinctrl/qcom/pinctrl-msm.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/pinctrl/qcom/pinctrl-msm.c b/drivers/pinctrl/qcom/pinctrl-msm.c
index 0e22f52b2a19..3563c4394837 100644
--- a/drivers/pinctrl/qcom/pinctrl-msm.c
+++ b/drivers/pinctrl/qcom/pinctrl-msm.c
@@ -626,6 +626,19 @@ static void msm_gpio_irq_mask(struct irq_data *d)
 	raw_spin_lock_irqsave(&pctrl->lock, flags);

 	val = readl(pctrl->regs + g->intr_cfg_reg);
+	/*
+	 * Leaving the RAW_STATUS_EN bit enabled causes level interrupts that
+	 * are still asserted to re-latch after we ack them. Clear the raw
+	 * status enable bit too so the interrupt can't even latch into the
+	 * hardware while it's masked, but only do this for level interrupts
+	 * because edge interrupts have a problem with the raw status bit
+	 * toggling and causing spurious interrupts.
+	 */
+	if (irqd_get_trigger_type(d) & IRQ_TYPE_LEVEL_MASK) {
+		val &= ~BIT(g->intr_raw_status_bit);
+		writel(val, pctrl->regs + g->intr_cfg_reg);
+	}
+
 	val &= ~BIT(g->intr_enable_bit);
 	writel(val, pctrl->regs + g->intr_cfg_reg);

@@ -647,6 +660,10 @@ static void msm_gpio_irq_unmask(struct irq_data *d)
 	raw_spin_lock_irqsave(&pctrl->lock, flags);

 	val = readl(pctrl->regs + g->intr_cfg_reg);
+	if (irqd_get_trigger_type(d) & IRQ_TYPE_LEVEL_MASK) {
+		val |= BIT(g->intr_raw_status_bit);
+		writel(val, pctrl->regs + g->intr_cfg_reg);
+	}
 	val |= BIT(g->intr_enable_bit);
 	writel(val, pctrl->regs + g->intr_cfg_reg);

-- 
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