OMAP: DSS2: Documentation for DSS2

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>

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+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>
+	- Amount of total VRAM to preallocate. 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
+