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

Coiby Xu coiby.xu at gmail.com
Fri Oct 2 10:59:06 UTC 2020

On Thu, Oct 01, 2020 at 10:57:40PM +0200, Linus Walleij wrote:
>Sorry for top posting, but I want to page some people.
>I do not know anything about ACPI, but Hans de Goede is really
>good with this kind of things and could possibly provide some

Thank you for introducing Hans de Goede to me!

>Linus Walleij
>On Thu, Oct 1, 2020 at 3:23 PM Coiby Xu <coiby.xu at gmail.com> wrote:
>> Hi,
>> I'm trying to fix broken touchpads [1] for a new laptop model Legion-5
>> 15ARH05 which is shipped with two different touchpads, i.e., ElAN and
>> Synaptics. For the ELAN touchpad, the kernel receives no interrupts to
>> be informed of new data from the touchpad. For the Synaptics touchpad,
>> only 7 interrupts are received per second which makes the touchpad
>> completely unusable. Based on current observations, pinctrl-amd seems to
>> be the most suspicious cause.
>> Why do I think pinctrl-amd smells the most suspicious?
>> ======================================================
>> This laptop model has the following hardware configurations specified
>> via ACPI,
>>   - The touchpad's data interrupt line is connected to pin#130 of a GPIO
>>     chip
>>          GpioInt (Level, ActiveLow, ExclusiveAndWake, PullUp, 0x0000,
>>                          "\\_SB.GPIO", 0x00, ResourceConsumer, ,
>>                          )
>>                          {   // Pin list
>>                              0x0082
>>                          }
>>   - This GPIO chip (HID: AMDI0030) which is assigned with IRQ#7 has its
>>     common interrupt output line connected to one IO-APIC's pin#7
>>          Interrupt (ResourceConsumer, Level, ActiveLow, Shared, ,, )
>>          {
>>              0x00000007,
>>          }
>> I add some code to kernel to poll the status of the GPIO chip's pin#130
>> and IO-APIc's pin#7 every 1ms when I move my finger on the surface of
>> the Synaptics touchpad continuously for about 1s. During the process of I
>> move my finger, most of the time,
>>   - GPIO chip's pin#130: low input, interrupt unmasked
>>   - IO-APIC's pin#7: IRR=0, interrupt unmasked (in fact mask/unmask_ioapic_irq
>>     have never been called by the IRQ follow controller handle_fasteoi_irq)
>> So the touchpad has been generating interrupts most of the time while
>> IO-APIC controller hasn't been masking the interrupt from the GPIO chip.
>> But somehow the kernel could only get ~7 interrupts each second while
>> the touchpad could generate 140 interrupts (time resolution of 7.2ms)
>> per second. Assuming IO-APIC (arch/x86/kernel/apic/io_apic.c) is fine,
>> then there's something wrong with the GPIO interrupt controller which
>> works fine for the touchpad under Windows. Besides if I poll the touchpad
>> data based on pin#130's status, the touchpad could also work under
>> Windows.
>> Ways to debug pinctrl-amd
>> =========================
>> I can't find any documentation about the AMDI0030 GPIO chip except for
>> the commit logs of drivers/pinctrl/pinctrl-amd. One commit
>> ba714a9c1dea85e0bf2899d02dfeb9c70040427c ("pinctrl/amd: Use regular interrupt instead of chained")
>> inspired me to bring back chained interrupt to see if "an interrupt storm"
>> would happen. The only change I noticed is that the interrupts arrive in
>> pairs. The time internal between two interrupts in a pair is ~0.0016s
>> but the time internal between interrupt pairs is still ~0.12s (~8Hz).
>> Unfortunately, I don't get any insight about the GPIO interrupt
>> controller from this tweaking. I wonder if there are any other ways
>> to debug drivers/pinctrl/pinctrl-amd?
>> Thank you!
>> [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1887190
>> --
>> Best regards,
>> Coiby

Best regards,

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