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weird backlight (brightness) changes on thinkpad t540p
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Anton Gubarkov
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Joined: 13 Mar 2008
Posts: 50

PostPosted: Wed May 14, 2014 7:31 pm    Post subject: weird backlight (brightness) changes on thinkpad t540p Reply with quote

when I boot my laptop (3.15.0-rc5, thinkpad_acpi, tlp), the brightness is changed to minimum very early in the boot process (before KMS modset). The brightness control buttons don't work until X/gdm is up.

Once I get X/gdm, I can control brightness.

Every switch from/to AC power brings my brightness to a minimum level. I can't figure out how to change this behaviour, I can't trace what process makes the change.

When I'm on AC and my battery is fully charged, the log shows a lot of the following events, and every time these series of events is logged, my brightness is reduced to a minimum value. It may happen several times per minute - very annoying.

May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru logger[5192]: ACPI event unhandled: ac_adapter ACPI0003:00 00000080 00000001
May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru kernel: thinkpad_ec: thinkpad_ec_request_row: arg0 rejected: (0x01:0x00)->0x00
May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru kernel: thinkpad_ec: thinkpad_ec_read_row: failed requesting row: (0x01:0x00)->0xfffffffb
May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru kernel: thinkpad_ec: initial ec test failed
May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru kernel: thinkpad_acpi: EC reports that Thermal Table has changed
May 14 23:22:43 r9-008cln.766.adsl.cifra1.ru logger[5261]: ACPI event unhandled: ibm/hotkey LEN0068:00 00000080 00006030
May 14 23:22:44 r9-008cln.766.adsl.cifra1.ru logger[5268]: ACPI event unhandled: thermal_zone LNXTHERM:00 00000081 00000000
May 14 23:22:44 r9-008cln.766.adsl.cifra1.ru logger[5271]: ACPI event unhandled: battery PNP0C0A:00 00000080 00000001
May 14 23:22:44 r9-008cln.766.adsl.cifra1.ru logger[5273]: ACPI event unhandled: battery PNP0C0A:00 00000080 00000001


I seek your advice on how to trace this erratic behaviour.
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