Re: [PATCH] ELAN touchpad i2c_hid bugs fix

From: Hans de Goede
Date: Fri Mar 29 2019 - 08:18:25 EST


On 3/25/19 5:56 PM, Dmitry Torokhov wrote:
Hi Hans,

On Mon, Mar 25, 2019 at 9:38 AM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:

Hi Dmitry,

On 25-03-19 17:02, Dmitry Torokhov wrote:
Hi Vladislav,

On Mon, Mar 25, 2019 at 5:57 AM Vladislav Dalechyn
<vlad.dalechin@xxxxxxxxx> wrote:

From: Vladislav Dalechyn <hotwater438@xxxxxxxxxxxx>

Description: The ELAN1200:04F3:303E touchpad exposes several issues, all
caused by an error setting the correct IRQ_TRIGGER flag:
- i2c_hid incoplete error flood in journalctl;
- Five finger tap kill's module so you have to restart it;
- Two finger scoll is working incorrect and sometimes even when you
raised one of two finger still thinks that you are scrolling.

Fix all of these with a new quirk that corrects the trigger flag
announced by the ACPI tables. (edge-falling).

I do not believe this is right solution. The driver makes liberal use
of disable_irq() and enable_irq() which may lead to lost edges and
touchpad stopping working altogether.

Usually the "extra" report is caused by GPIO controller clearing
interrupt condition at the wrong time (too early), or in unsafe or
racy fashion. You need to look there instead of adding quirk to

The falling-edge solution was proposed by Elan themselves.

Also if you look at:

And esp. the "cat /proc/interrupts" output there, then you will see
that the interrupt seems to be stuck at low level, which according
to the ACPI tables is its active level.

So how does it generate a new edge if it is stuck at low?

Is it bad touchpad firmware that does not deassert interrupt quickly

I do not believe it is not de-asserting it quick enough (I believe
the amount of interrups is too high for that.

It seems to simply be low most of the time, or it is really really
slow with de-asserting.

Vladislav can you check the output of /cat/interrupts on a kernel
without the patch and while *not* using the touchpad; and check
if the amount of touchpads-interrupts still keeps increasing in this

Also I believe that you had contact with Elan about this and they
told you to change the interrupt type to falling-edge as work-around,
right? Can you ask them why?

This is quite unususal, I've collected quite a few DSDTs over time
and I've just checked about 40 of them all with a PNP0C50 in
some form (and in many cases multiple such devices) and NONE of
them is using edged-interrupts in the ACPI config.


I think that the Elan touchpad firmware supports a mode to
work on devices which only support edge interrupts and that
this mode is accidentally enabled in this firmware.

I think that the interrupt line is simply low all the time
and gets pulsed high then low again when the touchpad detects
a finger. Hopefully it does this pulsing on every event and not
only when its event "fifo" is empty.


I scrolled through the bug but I do not see if it had been
confirmed that original windows installation actually uses edge (it
may very well be using it; Elan engineers pushed us to use edge in a
few cases, but they all boiled down to an issue with pin control/GPIO

This has not been checked on Windows AFAIK.

As for this being a GPIO chip driver problem, this is using standard
Intel pinctrl stuff, which is not showing this same issue with many
other i2c-hid touchpads.

Well, there have been plenty of issues in intel drivers, coupled with
"interesting" things done by firmware and boards.

If you want to keep on using edge you need to make sure that i2c-hid
never loses edge, as replaying of previously disabled interrupts in
not at all reliable. So you need to "kick" the device after
enable_irq() by initiating read from it and be ready to not get any
data or get valid data and process accordingly.

That is a good point and I agree.

Vladislav, let me explain this a bit. Normally the touchpad
driver the IRQ line low when it has touch-data to respond, which means
that if touch-data is reported before the driver loads (or while
the driver has the irq disabled during e.g. suspend), it will immediately
see an interrupt. If we use edge mode then the IRQ will only trigger
when the IRQ line goes from high to low, if this happens when the driver
is not listening then we do not see the edge. And since we never read the
pending touch-data, the IRQ line never goes high again (which it does
when we have read all available data), so we will never see a negative-edge
and then things are stuck.

It would be good, if running a kernel with your patch, you can try
to trigger this by:

1) Suspending the machine by selecting suspend from a menu in your
desktop environment, or by briefly pressing the power-button, do
not close the lid
2) As soon as the system starts suspending and while it is suspended, move
your finger around the touchpad
3) Wake the system up with the powerbutton while moving your finger around
4) Check if the touchpad still works after this

Or by:

1) Using ctrl + alt + f3 to switch to a text console
2) Move finger around on touchpad, keep moving it around
3) Switch back to X11 with alt + f2 or alt + f7, while still moving the finger
4) Check if the touchpad still works after this

If neither causes the touchpad to stop working, then at least the problem Dmitry
fears is not easy to trigger, but we should probably still prepare to deal
with it; and we really should try to better understand the problem here, so
if you can answer my questions above, then that would be great.