path: root/Documentation
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authorThomas Renninger <>2008-08-01 17:37:55 +0200
committerLen Brown <>2008-11-07 23:57:55 -0500
commitc3d6de698c84efdbdd3781b7058bcc339ab43da8 (patch)
tree07e08d88bbaaef8a5a1dd58b9d19f7c860442d3a /Documentation
parent22c13f9d8179f4c9caecfcb60a95214562b9addc (diff)
ACPI video: if no ACPI backlight support, use vendor drivers
If an ACPI graphics device supports backlight brightness functions (cmp. with latest ACPI spec Appendix B), let the ACPI video driver control backlight and switch backlight control off in vendor specific ACPI drivers (asus_acpi, thinkpad_acpi, eeepc, fujitsu_laptop, msi_laptop, sony_laptop, acer-wmi). Currently it is possible to load above drivers and let both poke on the brightness HW registers, the video and vendor specific ACPI drivers -> bad. This patch provides the basic support to check for BIOS capabilities before driver loading time. Driver specific modifications are in separate follow up patches. "acpi_backlight=vendor" Prever vendor driver over ACPI driver for backlight. "acpi_backlight=video" (default) Prever ACPI driver over vendor driver for backlight. Signed-off-by: Thomas Renninger <> Acked-by: Zhang Rui <> Signed-off-by: Andi Kleen <> Signed-off-by: Len Brown <>
Diffstat (limited to 'Documentation')
1 files changed, 12 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c86c07459712..dd5013f974d8 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -198,6 +198,18 @@ and is between 256 and 4096 characters. It is defined in the file
that require a timer override, but don't have
+ acpi_backlight= [HW,ACPI]
+ acpi_backlight=vendor
+ acpi_backlight=video
+ If set to vendor, prefer vendor specific driver
+ (e.g. thinkpad_acpi, sony_acpi, etc.) instead
+ of the ACPI video.ko driver.
+ acpi_display_output= [HW,ACPI]
+ acpi_display_output=vendor
+ acpi_display_output=video
+ See above.
acpi.debug_layer= [HW,ACPI]
Format: <int>
Each bit of the <int> indicates an ACPI debug layer,