Re: [PATCH] HID: i2c-hid: acpi: Add Dell Latitude 7400 2-in-1 touchscreen power quirk

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, Nov 10, 2026 at 04:08:04PM +0000, HoroTW wrote:
> On the Dell Latitude 7400 2-in-1, the Wacom touchscreen (WCOM48CA) does
> not work after resume from S3. Resume runs into I2C timeouts for 4 to 37
> seconds and then fails:
> 
>   [37928.985861] i2c_designware i2c_designware.0: controller timed out
>   [37928.986100] i2c_hid_acpi i2c-WCOM48CA:00: failed to change power setting.
>   [37928.986340] i2c_hid_acpi i2c-WCOM48CA:00: PM: dpm_run_callback(): acpi_subsys_resume returns -110
> 
> The controller has a power enable on GPP_B21 and an active-low reset on
> GPP_B15.

Oh, cool! Do you have access to the schematics?

> The firmware sets both up at boot, but ACPI does not describe
> them: TPL0's _CRS only lists the I2C bus and the interrupt, and there is
> no _PS0, _PS3 or _PR0. After S3 the firmware leaves both pads low, so
> the controller stays unpowered and in reset. pinctrl-intel does not
> restore them either, as it only saves pads that the kernel has requested.

Oh, can you bring the excerpts from /sys/kernel/debug/pinctrl/*/pins file
for B21 and B15 before the suspend (working case) and after (non-working),
so we can see their configurations?

> Add a DMI quirk that provides the two GPIOs through a GPIO lookup table,
> and power_up()/power_down() callbacks that sequence them like i2c-hid-of
> does: power on, wait, release reset, wait. Holding the GPIOs from probe
> makes pinctrl-intel save and restore the pads, and power_down() drives
> them low first, so power_up() always starts from the powered-down state.
> 
> As far as I can tell from the BIOS image, the firmware waits about 9 ms
> after enabling power before pulsing reset, so use 10 ms. Starting the
> first transfer less than 3 ms after releasing reset makes SET_POWER fail
> with -121, while 100 ms and 1000 ms both work; use 200 ms for some
> margin, as I could not find a datasheet value.
> 
> As the touchscreen is not a wakeup source, the controller is now also
> powered down in s2idle and for hibernation.

> Tested on a Latitude 7400 2-in-1 (BIOS 1.39.1) in S3, s2idle and
> hibernation (pm_test=devices).

> AI notice: I threw an AI coding agent against it which wrote most of
> the initial patch, I reviewed everything, directed the investigation
> and ensured this is a minimal patch. The agent ran the initial tests
> (via a KVM switch), and I tested it on the device myself as well.

For now this paragraph should go after '---' line below.

> Signed-off-by: HoroTW <git@horotw.dev>
> ---
> 
> Notes:
>     This is my first kernel patch, so sorry in advance for anything I got
>     wrong; I would be glad about any feedback.. I tried hard to match the
>     required ettiquete.
>     
>     Background: the Latitude 7400 2-in-1 is a nice device, but it has
>     issues with S3 sleep. As I did not have much time, I threw an AI coding
>     agent on it and steered it in the directions that looked promising,
>     until it found out what goes wrong and how it could be fixed.
>     I reviewed all of the code and tried to keep the patch minimal,
>     while keeping it readable and oriented me on how similar cases were
>     handled before.
>     
>     - I looked at i2c-hid-dmi-quirks.c and tried to follow its pattern (DMI
>       match, then device name), but kept the table in i2c-hid-acpi.c, as
>       only this driver uses it, and did not add a bigger structure for a
>       single device. My thought was that if more models need this, the
>       delays could move into the DMI match data, as i2c-hid-of-elan keeps
>       them per compatible. I'm happy to rework it if you would prefer it
>       differently, e.g. in i2c-hid-dmi-quirks.c or drivers/platform/x86.
>     
>     - The GPIOs are only requested for the quirked device and with named
>       con_ids, so as far as I understand, gpiolib-acpi will not fall back
>       to _CRS and pick up the touchscreen's GpioInt.
>     
>     - I did not add checks for the return values of the GPIO writes in
>       power_up(), following i2c-hid-of; i2c_hid_core_resume() ignores the
>       return value of power_up() anyway.
>     
>     - Only the Wacom WCOM48CA panel was tested. The DSDT can also describe
>       other panels in the TPL0 node; this quirk does not cover them.
>     
>     - Test setup: Latitude 7400 2-in-1 (SKU 08E2, board 0HCNR3, Core
>       i5-8365U, touch controller 056A:48CA), BIOS 1.39.1. S3 works with the
>       BIOS "Sleep Mode" set to "Force S3" as well as "OS Automatic
>       Selection". Kernel v7.2.14 with i2c-hid.ko and i2c-hid-acpi.ko rebuilt
>       with this patch: 7 S3 and 5 s2idle cycles, hibernation freeze/restore
>       (pm_test=devices) and a driver reload. After every resume the touch
>       resume callback returned 0 in about 315 ms and the controller answered
>       HID GET_REPORT; finger input worked after S3. Without the patch, one
>       S3 cycle reproduced the failure. The patch builds cleanly on v7.4-rc2
>       with W=1 and sparse.
>     
>     - I was not sure whether this is suitable for stable... (I think it is?),
>       so I did not add a Cc: stable tag and would leave that to you.

-- 
With Best Regards,
Andy Shevchenko