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diff --git a/Documentation/arm/omap/dss.rst b/Documentation/arm/omap/dss.rst new file mode 100644 index 000000000000..a40c4d9c717a --- /dev/null +++ b/Documentation/arm/omap/dss.rst @@ -0,0 +1,372 @@ +========================= +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. + +omapdss driver support for audio +-------------------------------- +There exist several display technologies and standards that support audio as +well. Hence, it is relevant to update the DSS device driver to provide an audio +interface that may be used by an audio driver or any other driver interested in +the functionality. + +The audio_enable function is intended to prepare the relevant +IP for playback (e.g., enabling an audio FIFO, taking in/out of reset +some IP, enabling companion chips, etc). It is intended to be called before +audio_start. The audio_disable function performs the reverse operation and is +intended to be called after audio_stop. + +While a given DSS device driver may support audio, it is possible that for +certain configurations audio is not supported (e.g., an HDMI display using a +VESA video timing). The audio_supported function is intended to query whether +the current configuration of the display supports audio. + +The audio_config function is intended to configure all the relevant audio +parameters of the display. In order to make the function independent of any +specific DSS device driver, a struct omap_dss_audio is defined. Its purpose +is to contain all the required parameters for audio configuration. At the +moment, such structure contains pointers to IEC-60958 channel status word +and CEA-861 audio infoframe structures. This should be enough to support +HDMI and DisplayPort, as both are based on CEA-861 and IEC-60958. + +The audio_enable/disable, audio_config and audio_supported functions could be +implemented as functions that may sleep. Hence, they should not be called +while holding a spinlock or a readlock. + +The audio_start/audio_stop function is intended to effectively start/stop audio +playback after the configuration has taken place. These functions are designed +to be used in an atomic context. Hence, audio_start should return quickly and be +called only after all the needed resources for audio playback (audio FIFOs, +DMA channels, companion chips, etc) have been enabled to begin data transfers. +audio_stop is designed to only stop the audio transfers. The resources used +for playback are released using audio_disable. + +The enum omap_dss_audio_state may be used to help the implementations of +the interface to keep track of the audio state. The initial state is _DISABLED; +then, the state transitions to _CONFIGURED, and then, when it is ready to +play audio, to _ENABLED. The state _PLAYING is used when the audio is being +rendered. + + +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 +output_type Output type (video encoder only): "composite" or "svideo" +=============== ============================================================= + +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 standard dma allocator. You +can enable Contiguous Memory Allocator (CONFIG_CMA) to improve the dma +allocator, and if CMA is enabled, you use "cma=" kernel parameter to increase +the global memory area for CMA. + +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 +--------------------- + +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 |