[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 12:42:35 UTC 2020

On Fri, Oct 02, 2020 at 11:40:12AM +0200, Hans de Goede wrote:
>On 10/1/20 10:57 PM, 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
>Thanks, although I'm honored to be considered the go to person
>for these kinda things my specialty really lies with these
>kinda issues with intel Bay Trail and Cherry Trail SoCs
>never the less let me take a look.

Thank you for taking time to examine this touchpad issue!

>>On Thu, Oct 1, 2020 at 3:23 PM Coiby Xu <coiby.xu at gmail.com> wrote:
>>>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,
>>>          }
>So these both look fine.
>>>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
>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.

>To me this sounds like the interrupt is configured as being triggered on
>a negative edge so that it only fires once when the line from the touchpad
>goes low, and for some reason 7 times a second the touchpad controller
>briefly releases the line (sorta gives up to signal the irq and then
>tries again?).
>>>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
>I agree that this sounds like a problem with the GpioInt handling.
>>>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?
>The way I would try to debug this (with access to the hardware) is
>to try an verify the interrupt trigger (level vs edge) settings inside
>pinctrl/amd by adding a bunch of printks printing them whenever the
>relevant register bits are touched.
>So I'm going to guess here that these touchpads use i2c-hid, so I
>took a quick peak at the i2c-hid irq request code from
>        unsigned long irqflags = 0;
>        int ret;
>        dev_dbg(&client->dev, "Requesting IRQ: %d\n", client->irq);
>        if (!irq_get_trigger_type(client->irq))
>                irqflags = IRQF_TRIGGER_LOW;
>        ret = request_threaded_irq(client->irq, NULL, i2c_hid_irq,
>                                   irqflags | IRQF_ONESHOT, client->name, ihid);
>So this tries to preserve the pre-configured irq-type on the irq
>line and if no irq-type is set then it overrides the trigger-type
>to IRQF_TRIGGER_LOW, which means level-low.
>One quick hack you can try is ommenting out the "if (!irq_get_trigger_type(client->irq))"
>type, I guess maybe the pinctrl-amd code is defaulting all IRQs to some
>edge trigger type? This should override it and recontrol it to
>a level trigger type.
Yes, "these touchpads use i2c-hid". I have examined the configuration of
irq-type in drivers/hid/i2c-hid/i2c-hid-core.c and can confirm it's been
configured to be level-low.

$ sudo cat /sys/kernel/debug/gpio|grep -A1 pin130
260:pin130      Level trigger| Active low| interrupt is enabled| interrupt is unmasked| disable wakeup in S0i3 state| disable wakeup in S3 state|

(Of course we rely on drivers/pinctrl/pinctrl-amd.c to read&interpret
data from the corresponding registers. If pinctrl-amd is return false
reports, we can do nothing about this)

Btw, we can't make any change in i2c-hid because they will be overridden
by drivers/pinctrl/pinctrl-amd.c which use the values from the ACPI tables

static int amd_gpio_irq_set_type(struct irq_data *d, unsigned int type)

	/* Ignore the settings coming from the client and
	 * read the values from the ACPI tables
	 * while setting the trigger type

	irq_flags = irq_get_trigger_type(d->irq);
	if (irq_flags != IRQ_TYPE_NONE)
		type = irq_flags;

Also, With CONFIG_GENERIC_IRQ_DEBUGFS enabled, `cat /sys/kernel/debug/irq/irqs/72`
also shows irq#72 (#72 is requested IRQ of this touchpad device) has the
expected irq-type,

$ cat /sys/kernel/debug/irq/irqs/72
handler:  handle_level_irq
device:   (null)
status:   0x00000508
istate:   0x00000020
ddepth:   0
wdepth:   0
dstate:   0x00402208

>As you said hopefully the IOApic code is fine. Notice that the ioapic
>irqchip driver does not allow configuring the trigger type.

Yes. unlike pinctrl-amd, arch/x86/kernel/apic/io_apic.c doesn't provide
`(struct irq_chip*)->irq_set_type`. I notice during the setting-up of
ia-apic, all pins are configured with edge-high according to the IRQ
redirection table which can be printed out with the "apic=debug" kernel

     .... IRQ redirection table:
     IOAPIC 0:
      pin00, disabled, edge , high, V(00), IRR(0), S(0), physical, D(00), M(0)

      pin06, enabled , edge , high, V(06), IRR(0), S(0), physical, D(00), M(0)
      pin07, disabled, edge , high, V(00), IRR(0), S(0), physical, D(00), M(0)

Later, I manually printed out the IRQ redirection table when processing
touchpad HID reports, pin07 (which is connected with the GPIO's common
interrupt output line) has adopted the expected configuration,

     pin07, enabled , level, low , V(07), IRR(1), S(0), physical, D(00), M(0)

Today I played with the "noapic" kernel parameter to use PIC mode
so we can confirm there is nothing wrong with io-apic. Unfortunately
the I2C adapter can't be set-up (the error is "controller timed out").
As a consequence, the touchpad as an I2C client won't work either.

And I can't find a way to disable APIC for Windows either.

>I guess
>this is not part of the ioapic spec and that the BIOS/firmware is setting
>the triggerlevel in a io-apic implementation specific way, so we better hope
>it is right. I have had the unfortunate experience to try and debug a wrong
>io-apic irq-pin trigger-type issue with TPMs in some Lenovo thinkpads and
>in the end only the Lenovo BIOS team could fix this.

If the same BIOS/firmware is setting the trigger level in a wrong way,
shouldn't we find the same issue under Windows? Btw, I've set
'acpi_osi="Windows 2015"'
as the kernel parameter before but I didn't notice any change.


Best regards,

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