Comment 27 for bug 1098216
Revision history for this message
| Seth Forshee (sforshee) wrote Re: Regression in brightness control on Lenovo Thinkpad X230 and X1 Carbon | #27 |
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0f7b58d
(Get the code!)
We already know what the offending commit is.
commit a57f7f9175b8ccb
Author: Bob Moore <email address hidden>
Date: Fri Aug 17 10:55:02 2012 +0800
ACPICA: Add Windows8/Server2012 string for _OSI method.
The problem is that when Linux starts reporting itself as Windows 8 some Lenovo firmware changes its behavior to indicate that the ACPI backlight interface reports 101 brightness levels (this is a requirement of Windows 8). But in reality the firmware ignores 85% of the values that it says are valid and only accepts the same 16 values that it says are valid when the OS reports it self as something other than Windows 8. Any other values are completely ignored.
I've gone back and forth with upstream on this issue, but the maintainers haven't been very responsive. I've got a patch series that's been sitting on the mailing list for a couple of weeks now without any review from the maintainers.