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Splash Screen
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The splash_screen_prepare() function is a weak function defined in
common/splash.c. It is called as part of the splash screen display
sequence. It gives the board an opportunity to prepare the splash
image data before it is processed and sent to the frame buffer by
U-Boot.  Define your own version to use this feature.

CONFIG_SPLASH_SOURCE

Use the splash_source.c library. This library provides facilities to declare
board specific splash image locations, routines for loading splash image from
supported locations, and a way of controlling the selected splash location
using the "splashsource" environment variable.

splashsource works as follows:
- If splashsource is set to a supported location name as defined by board code,
  use that splash location.
- If splashsource is undefined, use the first splash location as default.
- If splashsource is set to an unsupported value, do not load a splash screen.

A splash source location can describe either storage with raw data, or storage
formatted with a file system. In case of a filesystem, the splash screen data is
loaded as a file. The name of the splash screen file can be controlled with the
environment variable "splashfile".