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

[Hans de Goede]

Hi,

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 ?

> P.S. Does RedHat have a representative in ASWG?

I think so yes, but mainly focussed on server related things I guess...

Regards,

Hans