[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 16:09:49 UTC 2020


On Tue, Oct 27, 2020 at 6:01 PM Hans de Goede <hdegoede at redhat.com> wrote:
> On 10/27/20 4:13 PM, Andy Shevchenko wrote:
> > 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.
>
> I see, so then the right thing to do for the bug which we are seeing
> on some AMD platforms would be to honor the debounce setting I guess ?
>
> Can you and/or Mika write a patch(set) for this ?

I will look at it, but meanwhile I would postpone until having a
Mika's Ack on the action that my understanding and course of actions
is correct.

> > P.S. Does RedHat have a representative in ASWG?
>
> I think so yes, but mainly focussed on server related things I guess...


-- 
With Best Regards,
Andy Shevchenko


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