[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 09:28:06 UTC 2020


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?



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