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 <trenn@suse.de>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

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
                         HPET
 
+        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,