ELAN i2c touchpad fail on warm reboot

ELAN i2c touchpad fail on warm reboot

[João Paulo Rechi Vita]

ELAN touchpads connected via i2c do not work correctly on a warm
reboot from a system that does not fully support them into linux
mainline. This is a somewhat esoteric bug, but it affects factory
production lines where a machine first boots some kind of flashing
tool / installer (which does not have proper support for this
touchpad) and then reboots into the installed system to run a factory
test procedure.

To reproduce it one needs a modified kernel where the touchpad is
driven by i2c_hid, so removing the ACPI HW id from
drivers/input/mouse/elan_i2c_core.c and removing the
USB_VENDOR_ID_ELAN entries from hid_ignore_list[] in
drivers/hid/hid-core.c should be enough. Then doing a warm reboot from
this modified kernel into mainline prevents the touchpad from working
at all, and dmesg gets flooded with these messages:

elan_i2c i2c-ELAN1000:00: invalid report id data (1)

Any ideas are welcome, and I can provide more data / run tests if needed.

This has been seen on the Asus E202SA, N552VW and X456UF.

Thanks and regards,

--
João Paulo Rechi Vita
http://about.me/jprvita
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