|Koen Kooi||Jan 28, 2009 1:42 am|
|Subject:||[beagleboard] DSS2 documentation|
|From:||Koen Kooi (ko...@beagleboard.org)|
|Date:||Jan 28, 2009 1:42:13 am|
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.
The DSS2 driver (omap-dss 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.
Working and tested features include:
- MIPI DPI (parallel) output - MIPI DSI output in command mode - MIPI DBI (RFBI) output (not tested for a while, might've gotten broken) - 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
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, omap-dss 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 visible to users except through omapfb driver. They register themselves to the DSS 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.
Currently there are no V4L2 display drivers planned, but it is possible to implement such either to omapfb driver, or as a separate one. From omap-dss point of view the V4L2 drivers should be similar to framebuffer driver.
Some clarification what the different components do:
- Framebuffer is a memory area inside OMAP's 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.
----- The sysfs interface is a hack, but works 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.
In /sys/devices/platform/omapfb we have four files: framebuffers, overlays, managers and displays. You can read them so see the current setup, and change them by writing to it in the form of "<item-id> <opt1>:<val1> <opt2>:<val2>..."
"framebuffers" lists all framebuffers. Its format is: <fb number> p:<physical address, read only> v:<virtual address, read only> s:<size, read only> t:<target overlay>
"overlays" lists all overlays. Its format is: <overlay name> t:<target manager> x:<xpos> y:<ypos> iw:<input width, read only> ih:<input height, read only> w:<output width> h:<output height> e:<enabled>
"managers" lists all overlay managers. Its format is: <manager name> t:<target display>
"displays" lists all displays. Its format is: <display name> e:<enabled> u:<update mode> t:<tear sync on/off> h:<xres/hfp/hbp/hsw> v:<yres/vfp/vbp/vsw> p:<pix clock, in kHz> m:<mode str, as in drivers/video/modedb.c:fb_find_mode>
There is also a debug sysfs file at /sys/devices/platform/omap-dss/clk which shows how DSS has configured the clocks.
In the example scripts "omapfb" is a symlink to /sys/devices/platform/ omapfb/.
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
Switch from LCD to DVI
dviline=`cat omapfb/displays |grep dvi` w=`echo $dviline | cut -d " " -f 5 | cut -d ":" -f 2 | cut -d "/" -f 1` h=`echo $dviline | cut -d " " -f 6 | cut -d ":" -f 2 | cut -d "/" -f 1`
echo "lcd e:0" > omapfb/displays echo "lcd t:none" > omapfb/managers fbset -fb /dev/fb0 -xres $w -yres $h # at this point you have to switch the dvi/lcd dip-switch from the omap board echo "lcd t:dvi" > omapfb/managers echo "dvi e:1" > omapfb/displays
After this the configuration looks like:
FB0 --- GFX -\ -- DVI FB1 --- VID1 --+- LCD -/ LCD FB2 --- VID2 -/ TV ----- TV
Clone GFX overlay to LCD and TV
tvline=`cat /sys/devices/platform/omapfb/displays |grep tv` w=`echo $tvline | cut -d " " -f 5 | cut -d ":" -f 2 | cut -d "/" -f 1` h=`echo $tvline | cut -d " " -f 6 | cut -d ":" -f 2 | cut -d "/" -f 1`
echo "1 t:none" > omapfb/framebuffers echo "0 t:gfx,vid1" > omapfb/framebuffers echo "gfx e:1" > omapfb/overlays echo "vid1 t:tv w:$w h:$h e:1" > omapfb/overlays echo "tv e:1" > omapfb/displays
After this the configuration looks like (only relevant parts shown):
FB0 +-- GFX ---- LCD ---- LCD \- VID1 ---- TV ---- TV
OMAP FB allocates the framebuffer memory using the OMAP VRAM allocator. If that fails, it will fall back to dma_alloc_writecombine().
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.
vram - Amount of total VRAM to preallocate. For example, "10M".
omapfb.video_mode - Default video mode for default display. For example, "800x400MR-24@60". See drivers/video/modedb.c
omapfb.vram - VRAM allocated for each framebuffer. Normally omapfb allocates vram depending on the display size. With this you can manually allocate more. For example "4M,3M" allocates 4M for fb0, 3M for fb1.
omapfb.debug - Enable debug printing. You have to have OMAPFB debug support enabled in kernel config.
omap-dss.def_disp - Name of default display, to which all overlays will be connected. Common examples are "lcd" or "tv".
omap-dss.debug - Enable debug printing. You have to have DSS debug support enabled in kernel config.
Error checking - Lots of checks are missing or implemented just as BUG()
Rotate (external FB) Rotate (VRFB) Rotate (SMS)
System DMA update for DSI - Can be used for RGB16 and RGB24P modes. Probably not for RGB24U (how to skip the empty byte?)
Power management - Context saving
Resolution change - The x/y res of the framebuffer are not display resolutions, but the size of the overlay. - The display resolution affects all planes on the display.
OMAP1 support - Not sure if needed