Add support for the new DMA2D features to the STM32F429i-Disco LTDC configuration. From Marco Krahl.

configs/stm32f429i-disco/ltdc/README.txt

@@ -10,6 +10,49 @@ cd tools
 cd ..
 make
 
+Note!
+In the current implementation the DMA2D driver only supports clut pixel format
+if the LTDC driver it does. Otherwise it will not be compatible with the nx
+framework. If CONFIG_FB_CMAP is configured, nx expects that any pixel format
+supports color lookup tables. This is also the case for non CLUT formats e.g.
+FB_FMT_RGB16_565. This may result in wrong color representation by nx if the
+pixel format is unequal to FB_FMT_RGB8.
+
+On the other hand layers with CLUT pixel format are not supported by the DMA2D
+controller, in the case they will be used as destination layer for the following
+operations:
+- blit
+- blend
+- fillarea
+
+To enable clut support in both LTDC and DMA2D driver the following
+configurations are valid:
+
+1.
+- Enable LTDC_INTERFACE and LAYER1/LAYER2
+- Layer1 FB_FMT_RGB8
+- Layer2 any non clut format
+
+But Layer2 can only be used as destination layer for dma2d operations above.
+This configuration is not compatibly to nx because LAYER2 will be referenced
+by up_fbgetvplane and is an invalid CLUT pixel format.
+
+2.
+- Enable LTDC_INTERFACE and LAYER1/LAYER2
+- Layer2 FB_FMT_RGB8
+- Layer1 any non clut format
+
+But Layer1 can only be used as destination layer for dma2d operations above.
+This configuration should be compatibly to nx because LAYER2 will be referenced
+by up_fbgetvplane and is an valid CLUT pixel format.
+
+All other non clut configuration work fine.
+
+If using the DMA2D controller without the LTDC controller e.g. camera interface
+than enable CONFIG_FB_CMAP and optional CONFIG_FB_TRANSPARENCY in your board
+specific configuration.
+
+
 Loading
 -----------------------------------------------
 st-flash write nuttx.bin 0x8000000
@@ -21,3 +64,7 @@ Interaction with NSH is via the serial console at 115200 8N1 baud.
 From the nsh comandline execute one (or both) of the examples:
 - nx (default nx example)
 - ltdc (trivial ltdc interface test)
+
+Note! The ltdc example ends in an infinite loop. To get control of the nsh
+start this example in the background with 'ltdc &'.
+