[Bug 72289] [GM45 backlight] LCD waterfall effect on HP 2230s laptop

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=72289

--- Comment #26 from Joonas Saarinen <jza at saunalahti.fi> ---
Here are some new results (I rebooted between each test).

1) Ubuntu Trusty kernel 3.13.0-19-generic
# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61250 0x80000000

No perceivable effect (waterfall effect remains).

2) Ubuntu Trusty kernel 3.13.0-19-generic
# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61254 0x15cc07c6 &&
intel_reg_write 0x61250 0xc0000000

The backlight works great.

3) The most recent upstream git Linux kernel
# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61250 0x80000000

The brightness adjustment has no effect, constantly maximum brightness.

4) The most recent upstream git Linux kernel
# intel_reg_write 0x61250 0x00000000 && intel_reg_write 0x61254 0x15cc07c6 &&
intel_reg_write 0x61250 0xc0000000

The backlight is stable. However the dynamic range is incorrect. The display
starts to dim when I go below about 40% brightness, all settings above that
correspond max brightness.

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