Re: [PATCH v2 3/3] pinctrl: qcom: Clear possible pending irq when remuxing GPIOs

From: Maulik Shah
Date: Thu Dec 03 2020 - 06:29:22 EST

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Hi Doug,

On 12/1/2020 3:14 AM, Doug Anderson wrote:

Hi,

On Mon, Nov 30, 2020 at 2:33 AM Maulik Shah <mkshah@xxxxxxxxxxxxxx> wrote:

[1] https://lore.kernel.org/r/603c691f-3614-d87b-075a-0889e9ffc453@xxxxxxxxxxxxxx

Please wait to land [1] before i confirm with HW team if this is indeed
valid case.

Oh, oops. Somehow I thought your reply was in response to patch #3 in
the series, not #1. I responded to patch #1 in the series now to make
it clear to wait for you.

@@ -187,15 +217,26 @@ static int msm_pinmux_set_mux(struct pinctrl_dev *pctldev,
if (WARN_ON(i == g->nfuncs))
return -EINVAL;

- raw_spin_lock_irqsave(&pctrl->lock, flags);
+ disable_irq(irq);

- val = msm_readl_ctl(pctrl, g);
+ raw_spin_lock_irqsave(&pctrl->lock, flags);
+ oldval = val = msm_readl_ctl(pctrl, g);
val &= ~mask;
val |= i << g->mux_bit;
msm_writel_ctl(val, pctrl, g);
-
raw_spin_unlock_irqrestore(&pctrl->lock, flags);

+ /*
+ * Clear IRQs if switching to/from GPIO mode since muxing to/from
+ * the GPIO path can cause phantom edges.
+ */
+ old_i = (oldval & mask) >> g->mux_bit;
+ if (old_i != i &&
+ (i == pctrl->soc->gpio_func || old_i == pctrl->soc->gpio_func))
+ msm_pinctrl_clear_pending_irq(pctrl, group, irq);
+

The phantom irq can come when switching to GPIO irq mode. so may be only
check if (i == pctrl->soc->gpio_func) {

Have you tested this experimentally?

Yes

I have experimentally tested this and I can actually see an interrupt
generated when I _leave_ GPIO as well as when I enter GPIO mode. If
you can't see this I can re-setup my test, but this was one of those
things that convinced me that the _transition_ is what was causing the
fake interrupt.

I think my test CL <https://crrev.com/c/2556012/> can help you with
testing if you wish.

even better if you can clear this unconditionally.

Why? It should only matter if we're going to/from GPIO mode.

Probably i was not clear, the phantom irq should be cleared when switching gpio to gpio IRQ mode.

When GPIO was used as Rx line in example QUP/UART use case, it can latch the phantom IRQ but as long as its IRQ is in disabled/masked state it doesn't matter.

its only when the GPIO is again set to IRQ mode with set_mux callback, the phantom IRQ needs clear to start as clean.

So we should check only for if (i == pctrl->soc->gpio_func) then clear phantom IRQ.

The same is case with .direction_output callback, when GPIO is used as output say as clock, need not clear any phantom IRQ,

The reason is with every pulse of clock it can latch as pending IRQ in GIC_ISPEND as long as it stay as output mode/clock.

its only when switching back GPIO from output direction to input & IRQ function, need to clear the phantom IRQ.

so we do not require clear phantom irq in .direction_output callback.

@@ -456,32 +497,49 @@ static const struct pinconf_ops msm_pinconf_ops = {
static int msm_gpio_direction_input(struct gpio_chip *chip, unsigned offset)
{
const struct msm_pingroup *g;
+ unsigned int irq = irq_find_mapping(chip->irq.domain, offset);
struct msm_pinctrl *pctrl = gpiochip_get_data(chip);
unsigned long flags;
+ u32 oldval;
u32 val;

g = &pctrl->soc->groups[offset];

+ disable_irq(irq);
+
raw_spin_lock_irqsave(&pctrl->lock, flags);

- val = msm_readl_ctl(pctrl, g);
+ oldval = val = msm_readl_ctl(pctrl, g);
val &= ~BIT(g->oe_bit);
msm_writel_ctl(val, pctrl, g);

raw_spin_unlock_irqrestore(&pctrl->lock, flags);

+ /*
+ * Clear IRQs if switching to/from input mode since that can use
+ * a phantom edge.
+ */
+ if (oldval != val)
+ msm_pinctrl_clear_pending_irq(pctrl, offset, irq);

same as above, can you clear this unconditionally.

Any reason why? If we didn't change anything then there's no reason
to go through all this extra code?

static int msm_gpio_direction_output(struct gpio_chip *chip, unsigned offset, int value)
{
const struct msm_pingroup *g;
+ unsigned int irq = irq_find_mapping(chip->irq.domain, offset);
struct msm_pinctrl *pctrl = gpiochip_get_data(chip);
unsigned long flags;
+ u32 oldval;
u32 val;

g = &pctrl->soc->groups[offset];

+ disable_irq(irq);
+
raw_spin_lock_irqsave(&pctrl->lock, flags);

val = msm_readl_io(pctrl, g);
@@ -491,12 +549,21 @@ static int msm_gpio_direction_output(struct gpio_chip *chip, unsigned offset, in
val &= ~BIT(g->out_bit);
msm_writel_io(val, pctrl, g);

- val = msm_readl_ctl(pctrl, g);
+ oldval = msm_readl_ctl(pctrl, g);

should be, oldval = val = msm_readl_ctl(pctrl, g);

otherwise val will carry invalid value.

Whoa! Good catch. How did I miss that and how did it not fail? I
will fix in a v3 but will wait until other questions are resolved
before sending.

val |= BIT(g->oe_bit);
msm_writel_ctl(val, pctrl, g);

raw_spin_unlock_irqrestore(&pctrl->lock, flags);

+ /*
+ * Clear IRQs if switching to/from input mode since that can use
+ * a phantom edge.
+ */
+ if (oldval != val)
+ msm_pinctrl_clear_pending_irq(pctrl, offset, irq);

i don't see a reason to clear the edges when switching to output mode.

can you remove the changes from .direction_output callback?

I haven't confirmed that this can glitch, however I did confirm that I
could glitch when muxing _away_ from GPIO mode. This makes me believe
that I could also glitch when muxing to an output.

I can try to concoct a test for this if necessary.

@@ -792,17 +859,6 @@ 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);
- }
-

Above change was clearing irq in .irq_enable callback which will do
clear + unmask from irq_startup() at the very end.
With your change, The problem is we have cleared the phantom irq much
earlier in __setup_irq() phase and in below case its still latched as
pending.

1. The client driver calls request_irq() => __setup_irq()
2. __setup_irq() then first invokes irq_request_resources() =>
msm_gpio_irq_reqres() => msm_pinmux_set_mux() =>
msm_pinctrl_clear_pending_irq()
3. __setup_irq() goes ahead and invokes __irq_set_trigger() =>
msm_gpio_irq_set_type()
4. __setup_irq() then invokes irq_startup() => gpiochip_irq_enable() =>
msm_gpio_irq_enable()

The phantom irq gets cleared in step (2) here, but with step (3) it gets
latched again and at the end of step (4) still get phantom irq.
This seems because as per below comment in driver, pasting the part
which has info,
/*
* The edge detection logic seems to have a problem where toggling the
RAW_STATUS_EN bit may
* cause the status bit to latch spuriously when there isn't any edge
*/
In step (3) msm_gpio_irq_set_type() touches the RAW_STATUS_EN making the
phantom irq pending again.
To resolve this, you will need to invoke msm_pinctrl_clear_pending_irq()
at the end of the msm_gpio_irq_set_type().

I would like Rajendra's (already in cc) review as well on above part.

Ugh, so we need a clear in yet another place. Joy. OK, I will wait
for Rajendra's comment but I can add similar code in
msm_gpio_irq_enable().

As the clearing phantom irq code in msm_gpio_irq_enable() is moved to separate function msm_pinctrl_clear_pending_irq(), it needs invoke from at the end of msm_gpio_irq_set_type() too.

Thanks,
Maulik

val = msm_readl_intr_cfg(pctrl, g);
val |= BIT(g->intr_raw_status_bit);
val |= BIT(g->intr_enable_bit);
@@ -815,14 +871,10 @@ static void msm_gpio_irq_clear_unmask(struct irq_data *d, bool status_clear)

static void msm_gpio_irq_enable(struct irq_data *d)
{
- struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
- struct msm_pinctrl *pctrl = gpiochip_get_data(gc);
-
if (d->parent_data)
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);

Still need the above if condition, the previous call
irq_chip_enable_parent() already enabled the IRQ at PDC and GIC, so only
go ahead to enable it at TLMM if there wasn't any parent.

if (!test_bit(d->hwirq, pctrl->skip_wake_irqs))
msm_gpio_irq_unmask(d);

Right. I'll fix it when I send the v3. Thanks!

-Doug

--
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