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

Hans de Goede hdegoede at redhat.com
Tue Oct 6 09:29:40 UTC 2020

On 10/6/20 11:28 AM, Hans de Goede wrote:
> Hi,
> On 10/6/20 10:55 AM, Hans de Goede wrote:
>> Hi,
>> On 10/6/20 10:31 AM, Coiby Xu wrote:
>>> On Tue, Oct 06, 2020 at 08:28:40AM +0200, Hans de Goede wrote:
>>>> Hi,
>>>> On 10/6/20 6:49 AM, Coiby Xu wrote:
>>>>> Hi Hans and Linus,
>>>>> I've found the direct evidence proving the GPIO interrupt controller is
>>>>> malfunctioning.
>>>>> I've found a way to let the GPIO chip trigger an interrupt by accident
>>>>> when playing with the GPIO sysfs interface,
>>>>>  - export pin130 which is used by the touchad
>>>>>  - set the direction to be "out"
>>>>>  - `echo 0 > value` will trigger the GPIO controller's parent irq and
>>>>>    "echo 1 > value" will make it stop firing
>>>>> (I'm not sure if this is yet another bug of the GPIO chip. Anyway I can
>>>>> manually trigger an interrupt now.)
>>>>> I wrote a C program is to let GPIO controller quickly generate some
>>>>> interrupts then disable the firing of interrupts by toggling pin#130's
>>>>> value with an specified time interval, i.e., set the value to 0 first
>>>>> and then after some time, re-set the value to 1. There is no interrupt
>>>>> firing unless time internal > 120ms (~7Hz). This explains why we can
>>>>> only see 7 interrupts for the GPIO controller's parent irq.
>>>> That is a great find, well done.
>>>>> My hypothesis is the GPIO doesn't have proper power setting so it stays
>>>>> in an idle state or its clock frequency is too low by default thus not
>>>>> quick enough to read interrupt input. Then pinctrl-amd must miss some
>>>>> code to configure the chip and I need a hardware reference manual of this
>>>>> GPIO chip (HID: AMDI0030) or reverse-engineer the driver for Windows
>>>>> since I couldn't find a copy of reference manual online? What would you
>>>>> suggest?
>>>> This sounds like it might have something to do with the glitch filter.
>>>> The code in pinctrl-amd.c to setup the trigger-type also configures
>>>> the glitch filter, you could try changing that code to disable the
>>>> glitch-filter. The defines for setting the glitch-filter bits to
>>>> disabled are already there.
>>> Disabling the glitch filter works like a charm! Other enthusiastic
>>> Linux users who have been troubled by this issue for months would
>>> also feel great to know this small tweaking could bring their
>>> touchpad back to life:) Thank you!
>> That is good to hear, I'm glad that we have finally found a solution.
>>> $ git diff
>>> diff --git a/drivers/pinctrl/pinctrl-amd.c b/drivers/pinctrl/pinctrl-amd.c
>>> index 9a760f5cd7ed..e786d779d6c8 100644
>>> --- a/drivers/pinctrl/pinctrl-amd.c
>>> +++ b/drivers/pinctrl/pinctrl-amd.c
>>> @@ -463,7 +463,7 @@ static int amd_gpio_irq_set_type(struct irq_data *d, unsigned int type)
>>>                  pin_reg &= ~(ACTIVE_LEVEL_MASK << ACTIVE_LEVEL_OFF);
>>>                  pin_reg |= ACTIVE_LOW << ACTIVE_LEVEL_OFF;
>>>                  pin_reg &= ~(DB_CNTRl_MASK << DB_CNTRL_OFF);
>>> -               pin_reg |= DB_TYPE_PRESERVE_HIGH_GLITCH << DB_CNTRL_OFF;
>>> +               /** pin_reg |= DB_TYPE_PRESERVE_HIGH_GLITCH << DB_CNTRL_OFF; */
>>>                  irq_set_handler_locked(d, handle_level_irq);
>>>                  break;
>>> I will learn more about the glitch filter and the implementation of
>>> pinctrl and see if I can disable glitch filter only for this touchpad.
>> The glitch filter likely also has settings for how long a glitch
>> lasts, which apparently goes all the way up to 120ms. If it would
>> only delay reporting by say 0.1ms and consider any pulse longer
>> then 0.1s not a glitch, then having it enabled would be fine.
>> I don't think we want some sort of quirk here to only disable the
>> glitch filter for some touchpads. One approach might be to simply
>> disable it completely for level type irqs.
>> What we really need here is some input from AMD engineers with how
>> this is all supposed to work.
>> E.g. maybe the glitch-filter is setup by the BIOS and we should not
>> touch it all ?
>> Or maybe instead of DB_TYPE_PRESERVE_HIGH_GLITCH low level interrupts
>> should use DB_TYPE_PRESERVE_LOW_GLITCH ?   Some docs for the hw
>> would really help here ...
> So I've been digging through the history of the pinctrl-amd.c driver
> and once upon a time it used to set a default debounce time of
> 2.75 ms.
> See the patch generated by doing:
> git format-patch 8cf4345575a416e6856a6856ac6eaa31ad883126~..8cf4345575a416e6856a6856ac6eaa31ad883126
> In a linux kernel checkout.
> So it would be interesting to add a debugging printk to see
> what the value of pin_reg & DB_TMR_OUT_MASK is for the troublesome
> I guess that it might be all 1s (0xfffffffff) or some such which
> might be a way to check that we should disable the glitch-filter
> for this pin?


Or maybe we should simply stop touching all the glitch-filter
related bits, in the same way as that old commit has already
removed the code setting the timing of the filter ?

At least is seems that forcing the filter to be on without
sanitizing the de-bounce time is not a good idea.



More information about the Linux-kernel-mentees mailing list