Brightness problem with Samsung NP470R5E

asked 2014-10-27 14:22:27 -0500

marcushall gravatar image

I'm having problems with my wife's notebook's brightness control. This seems to have started with the 3.16 kernel. There does seem to be an issue with the 3.15 kernel, but the impact isn't as severe.

It seems that once she has logged onto the system, the brightness adjustment key appears to trigger the ACPI functions correctly (the brightness icon appears and an indicator seems to move left and right), but there is no aparent change in brightness until the very last step, when the brightness falls down to zero. This behavior seems to be the case in the 3.15 kernel as well, but the difference is that in 3.16 the "on" setting is only about 50% bright, while with the 3.15 kernel the "on" setting seems to be full brightness.

If I look at /sys/class/backlight/intel_backlight, I see that max_brightness returns "4650".. OK, then if I echo anything to "brightness" down to "1", there is no effect. "0" turns it off, and "1' turns it back on again.

When booting, the screen dims to 50% when grub2 starts. When the grub page is displayed, I can use the keyboard keys to adjust the brightness, and if I crank it up there, it seems to carry over when booting into the 3.16 kernel. When booting to the 3.15 kernel, the screen dims when grub2 starts, then brightens back up when the kernel starts booting (fairly early in the boot sequence). With lxdm running, I cannot adjust the brightness via the keyboard, although I imagine that I could adjust the /sys file OK (haven't ssh'd into the system at that point to try). So, it seems that the 3.15 kernel used to reinitialize something with the backlight that the 3.16 kernel no longer does, and grub2 is initially bringing the backlight to dim...

I have seen a couple of suggestions to set "acpi_osi=linux" and "acip_brightness=vendor", but neither seems to have any effect on the 3.16 kernel (well, neigther kernel, I guess.).

Any suggestions on how to proceed??

TIA marcus hall marcus@tuells.org

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davidva gravatar imagedavidva ( 2014-10-28 01:08:24 -0500 )edit