Bootargs for enabling display omap

This articles talks about bootargs required to be added for enabling DSS. Starting with 2.6.34 (or L24.7) although DSS is enabled in defconfig, one needs to add some boot arguments to enable display and see penguin logos at the bootup time (skip to 27 min:14sec)

 

 

OMAP Display OVERLAYS

Overlay here means a software overlay. In hardware it is called as pipeline. 
-- Number of overlays for OMAP3: 3 
overlay0: GFX, 
overlay1: VID1, 
overlay2: VID2 

-- Number of overlays for OMAP4: 4 
overlay0: GFX, 
overlay1: VID1, 
overlay2: VID2 
overlay3: VID3 

[edit] Set overlay properties

• Set overlay0 ON:

echo "1" > /sys/devices/platform/omapdss/overlay0/enabled  

• Set overlay0 OFF:

echo "0" > /sys/devices/platform/omapdss/overlay0/enabled  

An overlay should be enabled if you want to see something on it.

[edit] Reading overlay properties

• Read overlay1 input size

cat /sys/devices/platform/omapdss/overlay0/input_size  

• Reading overlay0's name

cat /sys/devices/platform/omapdss/overlay0/name  

• Reading output_size of overlay0

cat /sys/devices/platform/omapdss/overlay0/output_size  

• Reading position of overlay0

cat /sys/devices/platform/omapdss/overlay0/position  

• Reading screen_width of overlay0

cat /sys/devices/platform/omapdss/overlay0/screen_width  

• Reading global_alpha of overlay0, Range: 0-255, 0=transparent 255=opaque

cat /sys/devices/platform/omapdss/overlay0/global_alpha  

[edit] Set overlay's manager

• Set overlay0's manager as lcd

echo "0" > /sys/devices/platform/omapdss/overlay0/enabled  echo "lcd" > /sys/devices/platform/omapdss/overlay0/manager  echo "1" > /sys/devices/platform/omapdss/overlay0/enabled  

 

Zorder of an overlay [Specific to OMAP4 Not Applicable to OMAP3]

An object with a Z-order of 1 would be visually "underneath" an object with a Z-order of 2 or greater.

The default zorders are:

Overlay 0 -> 0 
Overlay 1 -> 1 
Overlay 2 -> 2 
Overlay 3 -> 3 

To change the zorder the following command can be used:

# Make GFX topmost:  echo "3" > /sys/devices/platform/omapdss/overlay0/zorder