[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 06:28:40 UTC 2020


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.



> Thank you!
> On Sun, Oct 04, 2020 at 01:16:44PM +0800, Coiby Xu wrote:
>> On Sun, Oct 04, 2020 at 07:03:40AM +0800, Coiby Xu wrote:
>>> On Sat, Oct 03, 2020 at 03:22:46PM +0200, Hans de Goede wrote:
>>>> Hi,
>>>> On 10/3/20 12:45 AM, Coiby Xu wrote:
>>>>> On Fri, Oct 02, 2020 at 09:44:54PM +0200, Hans de Goede wrote:
>>>>>> Hi,
>>>>>> On 10/2/20 4:51 PM, Coiby Xu wrote:
>>>>>>> On Fri, Oct 02, 2020 at 03:36:29PM +0200, Hans de Goede wrote:
>>>>>> <snip>
>>>>>>>>>> So are you seeing these 7 interrupts / second for the touchpad irq or for
>>>>>>>>>> the GPIO controllers parent irq ?
>>>>>>>>>> Also to these 7 interrupts/sec stop happening when you do not touch the
>>>>>>>>>> touchpad ?
>>>>>>>>> I see these 7 interrupts / second for the GPIO controller's parent irq.
>>>>>>>>> And they stop happening when I don't touch the touchpad.
>>>>>>>> Only from the parent irq, or also on the touchpad irq itself ?
>>>>>>>> If this only happens on the parent irq, then I would start looking at the
>>>>>>>> amd-pinctrl code which determines which of its "child" irqs to fire.
>>>>>>> This only happens on the parent irq. The input's pin#130 of the GIPO
>>>>>>> chip is low most of the time and pin#130.
>>>>>> Right, but it is a low-level triggered IRQ, so when it is low it should
>>>>>> be executing the i2c-hid interrupt-handler. If it is not executing that
>>>>>> then it is time to look at amd-pinctrl's irq-handler and figure out why
>>>>>> that is not triggering the child irq handler for the touchpad.
>>>>> I'm not sure if I have some incorrect understandings about GPIO
>>>>> interrupt controller because I don't quite follow your reasoning.
>>>>> What I actually suspect is there's something wrong with amd-pinctrl
>>>>> which makes the GPIO chip fail to assert its common interrupt output
>>>>> line connected to one IO-APIC's pin#7 thus IRQ#7 fails to fire. What
>>>>> I learn about this low-level triggered IRQ is that the i2c-hid
>>>>> interrupt-handler will be woken up by amd-pinctrl's irq-handler which
>>>>> is executed when the parent IRQ#7 fires. The code path is as follows,
>>>>>     <IRQ>
>>>>>     dump_stack+0x64/0x88
>>>>>     __irq_wake_thread.cold+0x9/0x12
>>>>>     __handle_irq_event_percpu+0x80/0x1c0
>>>>>     handle_irq_event+0x58/0xb0
>>>>>     handle_level_irq+0xb7/0x1a0
>>>>>     generic_handle_irq+0x4a/0x60
>>>>>     amd_gpio_irq_handler+0x15f/0x1b0 [pinctrl_amd]
>>>>>     __handle_irq_event_percpu+0x45/0x1c0
>>>>>     handle_irq_event+0x58/0xb0
>>>>>     handle_fasteoi_irq+0xa2/0x210
>>>>>     do_IRQ+0x70/0x120
>>>>>     common_interrupt+0xf/0xf
>>>>>     </IRQ>
>>>>> But the problem is somehow IRQ#7 doesn't even fire when the input's
>>>>> pin#130 of the GIPO is low. Without IRQ#7 firing, amd-pinctrl's
>>>>> irq-handler wouldn't be executed in the first place, let alonet
>>>>> triggering the child irq handler. Btw, amd-pinctrl's irq-handler
>>>>> simply iterate over all pins. If there is mapped irq found for this
>>>>> hwirq (yes, it won't even check if this pin triggers the interrupt),
>>>>> then it will call generic_handle_irq. So there's nothing wrong about
>>>>> this part of code.
>>>> Ok, so the i2c-hid irq does fire, but only 7 times a second just
>>>> like the GPIO controller's parent irq.
>>> I'm not sure if it's correct to say if hi2c-hid irq fires or not and how
>>> frequently it fires since the i2c-hid irq is mapped to pin#130 of the
>>> GPIO interrupt controller and the touchpad has another interrupt line
>>> connected to pin#130 which fires to indicate new data. All we know is
>>> pin#130 of the GPIO chip has low input most of the time when the finger
>>> is on the touchpad so we can infer the touchpad has been trying to
>>> notify the kernel of new data but somehow GPIO's parent irq only fires 7
>>> times / second.
>>>> The only thing I can think of then is to add printk-s to check how
>>>> long the i2c-hid interrupt handler takes to complete. It could be
>>>> there is a subtle bug somewhere causing the i2c transfers to take
>>>> longer when run from a (threaded) irq handler. That would be weird
>>>> though, so I don't expect this to result in any useful findings.
>>> I also doubted if it takes too much time for the i2c-hid handler to
>>> finish reading i2c transfer, processing data and delivering to the input
>>> system. After measuring the time internal between the starting of the
>>> GPIO irq's parent handler and when pin#130 is unmasked, we can exclude
>>> this possibility.
>>> I have been wondering if we let make pin#130 have low input thus to
>>> trigger a interrupt firing or assert the GPIO's common interrupt output
>>> line manually thus we can measure how long does it take for the kernel
>>> to receive the signal. But once GPIO's pin is programmed to be a
>>> interrupt line we can't write anything to it and it seems other
>>> interrupts can only be generated by the hardware. So this idea is not
>>> plausible
>> Btw, there are other users who have the same laptop model but with a
>> different touchpad (ELAN). Their touchpads would show in
>> /proc/bus/input/devices but are completely dead. hid-recorder which
>> will read HID reports from /dev/hidraw gets nothing if they put there
>> fingers on the touchpad but the polling mode could also save their
>> touchpads. It seems GPIO controller's parent irq for the ELAN touchpad
>> doesn't even fire once. And unlike GPIO, IO-APIC has also be used by
>> other devices like the keyboard. So maybe it's safe to assert the root
>> cause is from the GPIO controller.
>>>> Other then that I'm all out of ideas I'm afraid.
>>> Thank you for taking time to investigate this issue anyway! Have a nice
>>> weekend:)
>>>> Regards,
>>>> Hans
>>> -- 
>>> Best regards,
>>> Coiby
>> -- 
>> Best regards,
>> Coiby
> -- 
> Best regards,
> Coiby

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