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

[Douglas Anderson]

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@xxxxxxxxxxxx>
---
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);
-	}
-
 	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);
 
-- 
2.29.2.576.ga3fc446d84-goog