It's bug in AtomBIOS or our reading AtomBIOS answer. My backlight is controlled by GPU so there are two important properties to check: 1) Is backlight control turned on 2) What level is used After booting backlight control is turned *off* and backlight value set to 0. Of course backlight level doesn't matter in that case, as backlight control is disabled. Backlight level is max in result. AtomBIOS ignores fact that backlight control is turned off, just reports backlight level (or not AtomBIOS, but out AtomBIOS parser hopefully). So after booting I have max backlight level and this: PANEL connected 1600x900+0+0 (normal left inverted right x axis y axis) 423mm x 238mm Backlight: 0 (0x00000000) range: (0,255) _PanningArea: _OutputNumber: 2 (0x00000002) ConnectorNumber: 2 (0x00000002) ConnectorType: Panel SignalFormat: LVDS supported: LVDS
This seems to be fixed by 392a13923eb4d44a8bdb204922230e126b188fae, but this commit introduces new bug to backlight control #24592. Just in case I reported that as two separated issues.
(In reply to comment #1) > This seems to be fixed by 392a13923eb4d44a8bdb204922230e126b188fae, but this > commit introduces new bug to backlight control #24592. That was not it. Bug #24592 is now fixed, but this is still valid.
We can't. With AtomBIOS we can only do so much - if AtomBIOS is lying to us regarding backlight there is not much we can do. This is why we use AtomBIOS as the very last resort after both direct HW access and ACPI have failed. The value read back should be OK after you have first set it. Of course we can set a fixed value if AtomBIOS reports 0 - this however will trigger other bug reports.
Created attachment 31263 [details] [review] Add RHD_CARD_FLAG_FORCEBL flag forcing on chip backlight control usage Then I'd like to propose this patch which introduces new flag for devices quirks.
Does this issue occur with the preferred ati driver (xf86-vide-ati)? If so, please move this to the Driver/Radeon component. Development of radeonhd has pretty much halted and development focus is on the ati driver. Please see http://www.x.org/wiki/radeonhd If the issue does not exist in the ati driver (or if there is no response to this message), this bug will be closed as WONTFIX unless someone contributes a patch.
(In reply to comment #5) > Does this issue occur with the preferred ati driver (xf86-vide-ati)? If so, > please move this to the Driver/Radeon component. How does radeon report backlight level according to you?
Not relevant for xf86-video-ati.
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