[Linux-kernel-mentees] Any other ways to debug GPIO interrupt controller (pinctrl-amd) for broken touchpads of a new laptop model?

Andy Shevchenko andy.shevchenko at gmail.com
Tue Oct 27 15:13:00 UTC 2020

On Tue, Oct 27, 2020 at 4:31 PM Hans de Goede <hdegoede at redhat.com> wrote:
> On 10/26/20 11:54 PM, Coiby Xu wrote:
> > Hi Hans and Linus,
> >
> > Will you interpret the 0x0000 value for debounce timeout in GPIO
> > Interrupt Connection Resource Descriptor as disabling debouncing
> > filter?
> >
> > GpioInt (EdgeLevel, ActiveLevel, Shared, PinConfig, DebounceTimeout, ResourceSource,
> > ResourceSourceIndex, ResourceUsage, DescriptorName, VendorData) {PinList}
> >
> > I'm not sure if Windows' implementation is the de facto standard like
> > i2c-hid. But if we are going to conform to the ACPI specs and we would
> > regard 0x0000 debounce timeout as disabling debouncing filter, then we
> > can fix this touchpad issue and potentially some related issues by
> > implementing the feature of supporting configuring debounce timeout in
> > drivers/gpio/gpiolib-acpi.c and removing all debounce filter
> > configuration in amd_gpio_irq_set_type of drivers/pinctrl/pinctrl-amd.c.
> > What do you think?
> >
> > A favorable evidence is I've collected five DSDT tables when
> > investigating this issue. All 5 DSDT tables have an GpioInt specifying
> > an non-zero debounce timeout value for the edge type irq and for all
> > the level type irq, the debounce timeout is set to 0x0000.
> That is a very interesting observation and this matches with my
> instincts which say that we should just disable the debounce filter
> for level triggered interrupts in pinctrl-amd.c
> Yes that is a bit of a shortcut vs reading the valie from the ACPI
> table, but I'm not sure that 0 always means disabled.
> Specifically the ACPI 6.2 spec also has a notion of pinconf settings
> and the docs on "PinConfig()"  say:
> Note: There is some overlap between the properties set by GpioIo/GpioInt/ PinFunction and
> PinConfig descriptors. For example, both are setting properties such as pull-ups. If the same
> property is specified by multiple descriptors for the same pins, the order in which these properties
> are applied is undetermined. To avoid any conflicts, GpioInt/GpioIo/PinFunction should provide a
> default value for these properties when PinConfig is used. If PinConfig is used to set pin bias,
> PullDefault should be used for GpioIo/GpioInt/ PinFunction. *If PinConfig is used to set debounce
> timeout, 0 should be used for GpioIo/GpioInt.*
> So that suggests that a value of 0 does not necessarily mean "disabled" but
> it means use a default, or possibly get the value from somewhere else such
> as from a ACPI PinConfig description (if present).

Nope, it was added to get rid of disambiguation when both Gpio*() and
PinConfig() are given.
So, 0 means default *if and only if* PinConfig() is present.

I.o.w. the OS layers should do this:

 - if Gpio*() provides Debounce != 0, we use it, otherwise
 - if PinConfig() is present for this pin with a debounce set, use it, otherwise
 - debounce is disabled.

Now we missed a midentry implementation in the Linux kernel, hence go
to last, i.e. disable debounce.
But it should be rather done in gpiolib-acpi.c.

Hope this helps.

I Cc'ed this to Mika as co-author of that part of specification, he
may correct me if I'm wrong.

P.S. Does RedHat have a representative in ASWG? If any ambiguity is
still present, feel free to propose ECR (IIRC abbreviation correctly)
to ASWG.

> So I see 2 ways to move forward with his:
> 1. Just disable the debounce filter for level type IRQs; or
> 2. Add a helper to sanitize the debounce pulse-duration setting and
>    call that when setting the IRQ type.
>    This helper would read the setting check it is not crazy long for
>    an IRQ-line (lets say anything above 1 ms is crazy long) and if it
>    is crazy long then overwrite it with a saner value.
> 2. is a bit tricky, because if the IRQ line comes from a chip then
> obviously max 1ms debouncing to catch eletrical interference should be
> fine. But sometimes cheap buttons for things like volume up/down on tablets
> are directly connected to GPIOs and then we may want longer debouncing...
> So if we do 2. we may want to limit it to only level type IRQs too.
> Note I have contacted AMD about this and asked them for some input on this,
> ideally they can tell us how exactly we should program the debounce filter
> and based on which data we should do that.

With Best Regards,
Andy Shevchenko

More information about the Linux-kernel-mentees mailing list