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Based on kernel version 3.2. Page generated on 2012-01-05 23:27 EST.

	OMAP2/3 Display Subsystem
	-------------------------
	
	This is an almost total rewrite of the OMAP FB driver in drivers/video/omap
	(let's call it DSS1). The main differences between DSS1 and DSS2 are DSI,
	TV-out and multiple display support, but there are lots of small improvements
	also.
	
	The DSS2 driver (omapdss module) is in arch/arm/plat-omap/dss/, and the FB,
	panel and controller drivers are in drivers/video/omap2/. DSS1 and DSS2 live
	currently side by side, you can choose which one to use.
	
	Features
	--------
	
	Working and tested features include:
	
	- MIPI DPI (parallel) output
	- MIPI DSI output in command mode
	- MIPI DBI (RFBI) output
	- SDI output
	- TV output
	- All pieces can be compiled as a module or inside kernel
	- Use DISPC to update any of the outputs
	- Use CPU to update RFBI or DSI output
	- OMAP DISPC planes
	- RGB16, RGB24 packed, RGB24 unpacked
	- YUV2, UYVY
	- Scaling
	- Adjusting DSS FCK to find a good pixel clock
	- Use DSI DPLL to create DSS FCK
	
	Tested boards include:
	- OMAP3 SDP board
	- Beagle board
	- N810
	
	omapdss driver
	--------------
	
	The DSS driver does not itself have any support for Linux framebuffer, V4L or
	such like the current ones, but it has an internal kernel API that upper level
	drivers can use.
	
	The DSS driver models OMAP's overlays, overlay managers and displays in a
	flexible way to enable non-common multi-display configuration. In addition to
	modelling the hardware overlays, omapdss supports virtual overlays and overlay
	managers. These can be used when updating a display with CPU or system DMA.
	
	Panel and controller drivers
	----------------------------
	
	The drivers implement panel or controller specific functionality and are not
	usually visible to users except through omapfb driver.  They register
	themselves to the DSS driver.
	
	omapfb driver
	-------------
	
	The omapfb driver implements arbitrary number of standard linux framebuffers.
	These framebuffers can be routed flexibly to any overlays, thus allowing very
	dynamic display architecture.
	
	The driver exports some omapfb specific ioctls, which are compatible with the
	ioctls in the old driver.
	
	The rest of the non standard features are exported via sysfs. Whether the final
	implementation will use sysfs, or ioctls, is still open.
	
	V4L2 drivers
	------------
	
	V4L2 is being implemented in TI.
	
	From omapdss point of view the V4L2 drivers should be similar to framebuffer
	driver.
	
	Architecture
	--------------------
	
	Some clarification what the different components do:
	
	    - Framebuffer is a memory area inside OMAP's SRAM/SDRAM that contains the
	      pixel data for the image. Framebuffer has width and height and color
	      depth.
	    - Overlay defines where the pixels are read from and where they go on the
	      screen. The overlay may be smaller than framebuffer, thus displaying only
	      part of the framebuffer. The position of the overlay may be changed if
	      the overlay is smaller than the display.
	    - Overlay manager combines the overlays in to one image and feeds them to
	      display.
	    - Display is the actual physical display device.
	
	A framebuffer can be connected to multiple overlays to show the same pixel data
	on all of the overlays. Note that in this case the overlay input sizes must be
	the same, but, in case of video overlays, the output size can be different. Any
	framebuffer can be connected to any overlay.
	
	An overlay can be connected to one overlay manager. Also DISPC overlays can be
	connected only to DISPC overlay managers, and virtual overlays can be only
	connected to virtual overlays.
	
	An overlay manager can be connected to one display. There are certain
	restrictions which kinds of displays an overlay manager can be connected:
	
	    - DISPC TV overlay manager can be only connected to TV display.
	    - Virtual overlay managers can only be connected to DBI or DSI displays.
	    - DISPC LCD overlay manager can be connected to all displays, except TV
	      display.
	
	Sysfs
	-----
	The sysfs interface is mainly used for testing. I don't think sysfs
	interface is the best for this in the final version, but I don't quite know
	what would be the best interfaces for these things.
	
	The sysfs interface is divided to two parts: DSS and FB.
	
	/sys/class/graphics/fb? directory:
	mirror		0=off, 1=on
	rotate		Rotation 0-3 for 0, 90, 180, 270 degrees
	rotate_type	0 = DMA rotation, 1 = VRFB rotation
	overlays	List of overlay numbers to which framebuffer pixels go
	phys_addr	Physical address of the framebuffer
	virt_addr	Virtual address of the framebuffer
	size		Size of the framebuffer
	
	/sys/devices/platform/omapdss/overlay? directory:
	enabled		0=off, 1=on
	input_size	width,height (ie. the framebuffer size)
	manager		Destination overlay manager name
	name
	output_size	width,height
	position	x,y
	screen_width	width
	global_alpha   	global alpha 0-255 0=transparent 255=opaque
	
	/sys/devices/platform/omapdss/manager? directory:
	display				Destination display
	name
	alpha_blending_enabled		0=off, 1=on
	trans_key_enabled		0=off, 1=on
	trans_key_type			gfx-destination, video-source
	trans_key_value			transparency color key (RGB24)
	default_color			default background color (RGB24)
	
	/sys/devices/platform/omapdss/display? directory:
	ctrl_name	Controller name
	mirror		0=off, 1=on
	update_mode	0=off, 1=auto, 2=manual
	enabled		0=off, 1=on
	name
	rotate		Rotation 0-3 for 0, 90, 180, 270 degrees
	timings		Display timings (pixclock,xres/hfp/hbp/hsw,yres/vfp/vbp/vsw)
			When writing, two special timings are accepted for tv-out:
			"pal" and "ntsc"
	panel_name
	tear_elim	Tearing elimination 0=off, 1=on
	
	There are also some debugfs files at <debugfs>/omapdss/ which show information
	about clocks and registers.
	
	Examples
	--------
	
	The following definitions have been made for the examples below:
	
	ovl0=/sys/devices/platform/omapdss/overlay0
	ovl1=/sys/devices/platform/omapdss/overlay1
	ovl2=/sys/devices/platform/omapdss/overlay2
	
	mgr0=/sys/devices/platform/omapdss/manager0
	mgr1=/sys/devices/platform/omapdss/manager1
	
	lcd=/sys/devices/platform/omapdss/display0
	dvi=/sys/devices/platform/omapdss/display1
	tv=/sys/devices/platform/omapdss/display2
	
	fb0=/sys/class/graphics/fb0
	fb1=/sys/class/graphics/fb1
	fb2=/sys/class/graphics/fb2
	
	Default setup on OMAP3 SDP
	--------------------------
	
	Here's the default setup on OMAP3 SDP board. All planes go to LCD. DVI
	and TV-out are not in use. The columns from left to right are:
	framebuffers, overlays, overlay managers, displays. Framebuffers are
	handled by omapfb, and the rest by the DSS.
	
	FB0 --- GFX  -\            DVI
	FB1 --- VID1 --+- LCD ---- LCD
	FB2 --- VID2 -/   TV ----- TV
	
	Example: Switch from LCD to DVI
	----------------------
	
	w=`cat $dvi/timings | cut -d "," -f 2 | cut -d "/" -f 1`
	h=`cat $dvi/timings | cut -d "," -f 3 | cut -d "/" -f 1`
	
	echo "0" > $lcd/enabled
	echo "" > $mgr0/display
	fbset -fb /dev/fb0 -xres $w -yres $h -vxres $w -vyres $h
	# at this point you have to switch the dvi/lcd dip-switch from the omap board
	echo "dvi" > $mgr0/display
	echo "1" > $dvi/enabled
	
	After this the configuration looks like:
	
	FB0 --- GFX  -\         -- DVI
	FB1 --- VID1 --+- LCD -/   LCD
	FB2 --- VID2 -/   TV ----- TV
	
	Example: Clone GFX overlay to LCD and TV
	-------------------------------
	
	w=`cat $tv/timings | cut -d "," -f 2 | cut -d "/" -f 1`
	h=`cat $tv/timings | cut -d "," -f 3 | cut -d "/" -f 1`
	
	echo "0" > $ovl0/enabled
	echo "0" > $ovl1/enabled
	
	echo "" > $fb1/overlays
	echo "0,1" > $fb0/overlays
	
	echo "$w,$h" > $ovl1/output_size
	echo "tv" > $ovl1/manager
	
	echo "1" > $ovl0/enabled
	echo "1" > $ovl1/enabled
	
	echo "1" > $tv/enabled
	
	After this the configuration looks like (only relevant parts shown):
	
	FB0 +-- GFX  ---- LCD ---- LCD
	     \- VID1 ---- TV  ---- TV
	
	Misc notes
	----------
	
	OMAP FB allocates the framebuffer memory using the OMAP VRAM allocator.
	
	Using DSI DPLL to generate pixel clock it is possible produce the pixel clock
	of 86.5MHz (max possible), and with that you get 1280x1024@57 output from DVI.
	
	Rotation and mirroring currently only supports RGB565 and RGB8888 modes. VRFB
	does not support mirroring.
	
	VRFB rotation requires much more memory than non-rotated framebuffer, so you
	probably need to increase your vram setting before using VRFB rotation. Also,
	many applications may not work with VRFB if they do not pay attention to all
	framebuffer parameters.
	
	Kernel boot arguments
	---------------------
	
	vram=<size>[,<physaddr>]
		- Amount of total VRAM to preallocate and optionally a physical start
		  memory address. For example, "10M". omapfb allocates memory for
		  framebuffers from VRAM.
	
	omapfb.mode=<display>:<mode>[,...]
		- Default video mode for specified displays. For example,
		  "dvi:800x400MR-24@60".  See drivers/video/modedb.c.
		  There are also two special modes: "pal" and "ntsc" that
		  can be used to tv out.
	
	omapfb.vram=<fbnum>:<size>[@<physaddr>][,...]
		- VRAM allocated for a framebuffer. Normally omapfb allocates vram
		  depending on the display size. With this you can manually allocate
		  more or define the physical address of each framebuffer. For example,
		  "1:4M" to allocate 4M for fb1.
	
	omapfb.debug=<y|n>
		- Enable debug printing. You have to have OMAPFB debug support enabled
		  in kernel config.
	
	omapfb.test=<y|n>
		- Draw test pattern to framebuffer whenever framebuffer settings change.
		  You need to have OMAPFB debug support enabled in kernel config.
	
	omapfb.vrfb=<y|n>
		- Use VRFB rotation for all framebuffers.
	
	omapfb.rotate=<angle>
		- Default rotation applied to all framebuffers.
		  0 - 0 degree rotation
		  1 - 90 degree rotation
		  2 - 180 degree rotation
		  3 - 270 degree rotation
	
	omapfb.mirror=<y|n>
		- Default mirror for all framebuffers. Only works with DMA rotation.
	
	omapdss.def_disp=<display>
		- Name of default display, to which all overlays will be connected.
		  Common examples are "lcd" or "tv".
	
	omapdss.debug=<y|n>
		- Enable debug printing. You have to have DSS debug support enabled in
		  kernel config.
	
	TODO
	----
	
	DSS locking
	
	Error checking
	- Lots of checks are missing or implemented just as BUG()
	
	System DMA update for DSI
	- Can be used for RGB16 and RGB24P modes. Probably not for RGB24U (how
	  to skip the empty byte?)
	
	OMAP1 support
	- Not sure if needed

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