ACPI: thinkpad-acpi: support 16 levels of brightness (v3)

Lenovo ThinkPads often have 16 brightness levels in EC, and not just eight
levels like older ThinkPads.  They also have standard ACPI backlight
brightness control.

We detect the number of brightness levels by the presence of a BCLL package
with 16 entries.  If BCLL is not there, we assume eight levels (Z6*).  If
it is there, but it doesn't have 16 entries, we assume eight levels (T60).
Otherwise we assume sixteen levels (T61, X61, etc).

We don't use _BCL because it can have side-effects in thinkpads.  Thanks to
Thomas Renninger <trenn@suse.de> for notifying me of this potential
problem.

Using the standard ACPI backlight brightness control *instead* of the
native thinkpad backlight control is a better idea, though.  A different
patch will take care of this.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 35 insertions, 26 deletions

diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index ec49926..a743bfa 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -923,19 +923,26 @@ sysfs backlight device "thinkpad_screen"
 This feature allows software control of the LCD brightness on ThinkPad
 models which don't have a hardware brightness slider.
 
-It has some limitations: the LCD backlight cannot be actually turned on or off
-by this interface, and in many ThinkPad models, the "dim while on battery"
-functionality will be enabled by the BIOS when this interface is used, and
-cannot be controlled.
-
-The backlight control has eight levels, ranging from 0 to 7.  Some of the
-levels may not be distinct.
-
-There are two interfaces to the firmware for brightness control, EC and CMOS.
-To select which one should be used, use the brightness_mode module parameter:
-brightness_mode=1 selects EC mode, brightness_mode=2 selects CMOS mode,
-brightness_mode=3 selects both EC and CMOS.  The driver tries to autodetect
-which interface to use.
+It has some limitations: the LCD backlight cannot be actually turned on or
+off by this interface, and in many ThinkPad models, the "dim while on
+battery" functionality will be enabled by the BIOS when this interface is
+used, and cannot be controlled.
+
+On IBM (and some of the earlier Lenovo) ThinkPads, the backlight control
+has eight brightness levels, ranging from 0 to 7.  Some of the levels
+may not be distinct.  Later Lenovo models that implement the ACPI
+display backlight brightness control methods have 16 levels, ranging
+from 0 to 15.
+
+There are two interfaces to the firmware for direct brightness control,
+EC and CMOS.  To select which one should be used, use the
+brightness_mode module parameter: brightness_mode=1 selects EC mode,
+brightness_mode=2 selects CMOS mode, brightness_mode=3 selects both EC
+and CMOS.  The driver tries to autodetect which interface to use.
+
+When display backlight brightness controls are available through the
+standard ACPI interface, it is best to use it instead of this direct
+ThinkPad-specific interface.
 
 Procfs notes:
 
@@ -947,11 +954,11 @@ Procfs notes:
 
 Sysfs notes:
 
-The interface is implemented through the backlight sysfs class, which is poorly
-documented at this time.
+The interface is implemented through the backlight sysfs class, which is
+poorly documented at this time.
 
-Locate the thinkpad_screen device under /sys/class/backlight, and inside it
-there will be the following attributes:
+Locate the thinkpad_screen device under /sys/class/backlight, and inside
+it there will be the following attributes:
 
 	max_brightness:
 		Reads the maximum brightness the hardware can be set to.
@@ -961,17 +968,19 @@ there will be the following attributes:
 		Reads what brightness the screen is set to at this instant.
 
 	brightness:
-		Writes request the driver to change brightness to the given
-		value.  Reads will tell you what brightness the driver is trying
-		to set the display to when "power" is set to zero and the display
-		has not been dimmed by a kernel power management event.
+		Writes request the driver to change brightness to the
+		given value.  Reads will tell you what brightness the
+		driver is trying to set the display to when "power" is set
+		to zero and the display has not been dimmed by a kernel
+		power management event.
 
 	power:
-		power management mode, where 0 is "display on", and 1 to 3 will
-		dim the display backlight to brightness level 0 because
-		thinkpad-acpi cannot really turn the backlight off.  Kernel
-		power management events can temporarily increase the current
-		power management level, i.e. they can dim the display.
+		power management mode, where 0 is "display on", and 1 to 3
+		will dim the display backlight to brightness level 0
+		because thinkpad-acpi cannot really turn the backlight
+		off.  Kernel power management events can temporarily
+		increase the current power management level, i.e. they can
+		dim the display.
 
 
 Volume control -- /proc/acpi/ibm/volume