Asus T300 CHI: Synaptics Touch Digitizer - missing at boot

[TJ]

Using 16.04 amd64 on an Asus T300 CHI 2-in-1 transformer-book (tablet + docking Bluetooth keyboard/trackpad).

At boot-time the USB-connected Synaptics touchscreen digitiser is not recognised but after an S3 sleep/resume it is. Smells like an ACPI issue but so far testing with and without acpi_osi="Windows 2013" (one of 2 OSI strings the ACPI DSDT recognises, and the most featureful of the two) has not solved it.

What is strange is the installer's 'Try Ubuntu' live session did have an active touchscreen.

[TJ (tj)]

It seems that the touchscreen digitiser is disabled if AC power is connected during boot-up. Leaving the AC plug disconnected and the touch is reliably available.

This definitely looks like an ACPI DSDT issue.

[TJ (tj)]

I've found a workaround that works reliably. Add to the kernel command-line:

acpi_osi=! acpi_osi="Windows 2013"

Edit "/etc/default/grub" to include those options in GRUB_CMDLINE_LINUX (there can be other options there too):

GRUB_CMDLINE_LINUX="debug acpi_osi=! acpi_osi=\"Windows 2013\""

Regenerate the GRUB config:

$ sudo update-grub

After a reboot the touchscreen should work and 'dmsg' (/var/log/kern.log) should include:

 ACPI: Disabled all _OSI OS vendors
...
 ACPI: Added _OSI(Windows 2013)
...
usb 1-7: new full-speed USB device number 5 using xhci_hcd
usb 1-7: New USB device found, idVendor=06cb, idProduct=11ef
usb 1-7: New USB device strings: Mfr=1, Product=2, SerialNumber=0
usb 1-7: Product: Synaptics Touch Digitizer V04
usb 1-7: Manufacturer: SYNAPTICS
...
input: SYNAPTICS Synaptics Touch Digitizer V04 as /devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/0003:06CB:11EF.0003/input/input11
input: SYNAPTICS Synaptics Touch Digitizer V04 Pen as /devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/0003:06CB:11EF.0003/input/input12
hid-multitouch 0003:06CB:11EF.0003: input,hiddev0,hidraw2: USB HID v1.11 Mouse [SYNAPTICS Synaptics Touch Digitizer V04] on usb-0000:00:14.0-7/input0

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "dmesg diff of failed vs working with AC connected" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]