| Message ID | 20201209163818.v3.1.I2702919afc253e2a451bebc3b701b462b2d22344@changeid |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3,1/3] irqchip: qcom-pdc: Fix phantom irq when changing between rising/falling | expand |
Quoting Douglas Anderson (2020-12-09 16:41:01) > We have a problem if we use gpio-keys and configure wakeups such that > we only want one edge to wake us up. AKA: > wakeup-event-action = <EV_ACT_DEASSERTED>; > wakeup-source; > > Specifically we end up with a phantom interrupt that blocks suspend if > the line was already high and we want wakeups on rising edges (AKA we > want the GPIO to go low and then high again before we wake up). The > opposite is also problematic. > > Specifically, here's what's happening today: > 1. Normally, gpio-keys configures to look for both edges. Due to the > current workaround introduced in commit c3c0c2e18d94 ("pinctrl: > qcom: Handle broken/missing PDC dual edge IRQs on sc7180"), if the > line was high we'd configure for falling edges. > 2. At suspend time, we change to look for rising edges. > 3. After qcom_pdc_gic_set_type() runs, we get a phantom interrupt. > > We can solve this by just clearing the phantom interrupt. > > NOTE: it is possible that this could cause problems for a client with > very specific needs, but there's not much we can do with this > hardware. As an example, let's say the interrupt signal is currently > high and the client is looking for falling edges. The client now > changes to look for rising edges. The client could possibly expect > that if the line has a short pulse low (and back high) that it would > always be detected. Specifically no matter when the pulse happened, > it should either have tripped the (old) falling edge trigger or the > (new) rising edge trigger. We will simply not trip it. We could > narrow down the race a bit by polling our parent before changing > types, but no matter what we do there will still be a period of time > where we can't tell the difference between a real transition (or more > than one transition) and the phantom. > > Fixes: f55c73aef890 ("irqchip/pdc: Add PDC interrupt controller for QCOM SoCs") > Signed-off-by: Douglas Anderson <dianders@chromium.org> > Reviewed-by: Maulik Shah <mkshah@codeaurora.org> > Tested-by: Maulik Shah <mkshah@codeaurora.org> > --- Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Hi, On Thu, Dec 10, 2020 at 1:56 PM Stephen Boyd <swboyd@chromium.org> wrote: > > Quoting Douglas Anderson (2020-12-09 16:41:03) > > Conceptually, we can envision the input on Qualcomm SoCs to pass > > through a bunch of blocks between coming into the chip and becoming a > > GPIO interrupt. From guessing and running a handful of tests, I > > believe that we can represent the state of the world with a drawing > > that looks something like this: > > > > +-----------------+ +-----------------+ +-----------------+ > > | INPUT | --> | PINMUX | | IS_INPUT | > > +-----------------+ | | --> | | > > | output bogus (?)| | output bogus (?)| > > | if not muxed | | if input disab. | > > +-----------------+ +-----------------+ > > | > > +---------------------------------------------------+--> to PDC > > | > > V > > +-----------------+ +-----------------+ +-----------------+ > > | INTR RAW ENABLE | | DETECTION LOGIC | | STATUS REGISTER | > > | | | | | | > > | output bogus (?)| --> | maybe handles | | latches inputs | > > | if disabled | | polarity diffs | --> | that are high | > > +-----------------+ | | | | > > | maybe debounces | | write 1 to clr | > > | level irqs | +-----------------+ > > +-----------------+ | > > | > > +---------------------------------------------------+ > > | > > V > > +-----------------+ > > | ENABLE | > > | | +-----------------+ > > | nothing passes | --> | SUMMARY IRQ | > > | through if | +-----------------+ > > | disabled | > > +-----------------+ > > This diagram doesn't make sense to me. I've gutted most of this code for v4 after Maulik pointed out why my testing was flawed. Hopefully v4 looks saner... -Doug
diff --git a/drivers/irqchip/qcom-pdc.c b/drivers/irqchip/qcom-pdc.c index bd39e9de6ecf..5dc63c20b67e 100644 --- a/drivers/irqchip/qcom-pdc.c +++ b/drivers/irqchip/qcom-pdc.c @@ -159,6 +159,8 @@ static int qcom_pdc_gic_set_type(struct irq_data *d, unsigned int type) { int pin_out = d->hwirq; enum pdc_irq_config_bits pdc_type; + enum pdc_irq_config_bits old_pdc_type; + int ret; if (pin_out == GPIO_NO_WAKE_IRQ) return 0; @@ -187,9 +189,26 @@ static int qcom_pdc_gic_set_type(struct irq_data *d, unsigned int type) return -EINVAL; } + old_pdc_type = pdc_reg_read(IRQ_i_CFG, pin_out); pdc_reg_write(IRQ_i_CFG, pin_out, pdc_type); - return irq_chip_set_type_parent(d, type); + ret = irq_chip_set_type_parent(d, type); + if (ret) + return ret; + + /* + * When we change types the PDC can give a phantom interrupt. + * Clear it. Specifically the phantom shows up when reconfiguring + * polarity of interrupt without changing the state of the signal + * but let's be consistent and clear it always. + * + * Doing this works because we have IRQCHIP_SET_TYPE_MASKED so the + * interrupt will be cleared before the rest of the system sees it. + */ + if (old_pdc_type != pdc_type) + irq_chip_set_parent_state(d, IRQCHIP_STATE_PENDING, false); + + return 0; } static struct irq_chip qcom_pdc_gic_chip = {
We have a problem if we use gpio-keys and configure wakeups such that we only want one edge to wake us up. AKA: wakeup-event-action = <EV_ACT_DEASSERTED>; wakeup-source; Specifically we end up with a phantom interrupt that blocks suspend if the line was already high and we want wakeups on rising edges (AKA we want the GPIO to go low and then high again before we wake up). The opposite is also problematic. Specifically, here's what's happening today: 1. Normally, gpio-keys configures to look for both edges. Due to the current workaround introduced in commit c3c0c2e18d94 ("pinctrl: qcom: Handle broken/missing PDC dual edge IRQs on sc7180"), if the line was high we'd configure for falling edges. 2. At suspend time, we change to look for rising edges. 3. After qcom_pdc_gic_set_type() runs, we get a phantom interrupt. We can solve this by just clearing the phantom interrupt. NOTE: it is possible that this could cause problems for a client with very specific needs, but there's not much we can do with this hardware. As an example, let's say the interrupt signal is currently high and the client is looking for falling edges. The client now changes to look for rising edges. The client could possibly expect that if the line has a short pulse low (and back high) that it would always be detected. Specifically no matter when the pulse happened, it should either have tripped the (old) falling edge trigger or the (new) rising edge trigger. We will simply not trip it. We could narrow down the race a bit by polling our parent before changing types, but no matter what we do there will still be a period of time where we can't tell the difference between a real transition (or more than one transition) and the phantom. Fixes: f55c73aef890 ("irqchip/pdc: Add PDC interrupt controller for QCOM SoCs") Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Maulik Shah <mkshah@codeaurora.org> Tested-by: Maulik Shah <mkshah@codeaurora.org> --- There are no dependencies between this patch and patch #2/#3. It can go in by itself. Patches are only grouped together in one series because they address similar issues. Maulik has got confirmation from hardware guys and understands the problem. This patch is ready to land. Changes in v3: - Adjusted the comment as per Maulik. Changes in v2: - 0 => false - If irq_chip_set_type_parent() fails don't bother clearing. - Add Fixes tag. drivers/irqchip/qcom-pdc.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-)