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| author | Carsten Emde <C.Emde@osadl.org> | 2012-03-15 15:56:25 +0100 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2013-04-25 20:25:44 +0100 |
| commit | f76bb07cf0f7dde553f141438261797f189ead5e (patch) | |
| tree | 1c24ae353f25f1e244bbd0503289192ce23dc520 /Documentation | |
| parent | e6742b3695b04303938c572261dd0b0e7e38396c (diff) | |
| download | lwn-f76bb07cf0f7dde553f141438261797f189ead5e.tar.gz lwn-f76bb07cf0f7dde553f141438261797f189ead5e.zip | |
drm/i915: panel: invert brightness via parameter
commit 7bd90909bbf9ce7c40e1da3d72b97b93839c188a upstream.
Following the documentation of the Legacy Backlight Brightness (LBB)
Register in the configuration space of some Intel PCI graphics adapters,
setting the LBB register with the value 0x0 causes the backlight to be
turned off, and 0xFF causes the backlight to be set to 100% intensity
(http://download.intel.com/embedded/processors/Whitepaper/324567.pdf).
The Acer Aspire 5734Z, however, turns the backlight off at 0xFF and sets
it to maximum intensity at 0. In consequence, the screen of this systems
becomes dark at an early boot stage which makes it unusable. The same
inversion applies to the BLC_PWM_CTL I915 register. This problem was
introduced in kernel version 2.6.38 when the PCI device of this system
was first supported by the i915 KMS module.
This patch adds a parameter to the i915 module to enable inversion of
the brightness variable (i915.invert_brightness).
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/kernel-parameters.txt | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index ddbf18eaaea4..d44116b70a6d 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -948,6 +948,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN capability is set. + i915.invert_brightness + [DRM] Invert the sense of the variable that is used to + set the brightness of the panel backlight. Normally a + value of 0 indicates backlight switched off, and the + maximum value sets the backlight to maximum brightness. + If this parameter is specified, a value of 0 sets the + backlight to maximum brightness, and the maximum value + switches the backlight off. + icn= [HW,ISDN] Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] |