diff options
Diffstat (limited to 'Documentation/devicetree/bindings/video/simple-framebuffer.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/video/simple-framebuffer.txt | 68 |
1 files changed, 64 insertions, 4 deletions
diff --git a/Documentation/devicetree/bindings/video/simple-framebuffer.txt b/Documentation/devicetree/bindings/video/simple-framebuffer.txt index 70c26f3a5b9a..4474ef6e0b95 100644 --- a/Documentation/devicetree/bindings/video/simple-framebuffer.txt +++ b/Documentation/devicetree/bindings/video/simple-framebuffer.txt @@ -1,8 +1,40 @@ Simple Framebuffer -A simple frame-buffer describes a raw memory region that may be rendered to, -with the assumption that the display hardware has already been set up to scan -out from that buffer. +A simple frame-buffer describes a frame-buffer setup by firmware or +the bootloader, with the assumption that the display hardware has already +been set up to scan out from the memory pointed to by the reg property. + +Since simplefb nodes represent runtime information they must be sub-nodes of +the chosen node (*). Simplefb nodes must be named "framebuffer@<address>". + +If the devicetree contains nodes for the display hardware used by a simplefb, +then the simplefb node must contain a property called "display", which +contains a phandle pointing to the primary display hw node, so that the OS +knows which simplefb to disable when handing over control to a driver for the +real hardware. The bindings for the hw nodes must specify which node is +considered the primary node. + +It is advised to add display# aliases to help the OS determine how to number +things. If display# aliases are used, then if the simplefb node contains a +"display" property then the /aliases/display# path must point to the display +hw node the "display" property points to, otherwise it must point directly +to the simplefb node. + +If a simplefb node represents the preferred console for user interaction, +then the chosen node's stdout-path property should point to it, or to the +primary display hw node, as with display# aliases. If display aliases are +used then it should be set to the alias instead. + +It is advised that devicetree files contain pre-filled, disabled framebuffer +nodes, so that the firmware only needs to update the mode information and +enable them. This way if e.g. later on support for more display clocks get +added, the simplefb nodes will already contain this info and the firmware +does not need to be updated. + +If pre-filled framebuffer nodes are used, the firmware may need extra +information to find the right node. In that case an extra platform specific +compatible and platform specific properties should be used and documented, +see e.g. simple-framebuffer-sunxi.txt . Required properties: - compatible: "simple-framebuffer" @@ -14,13 +46,41 @@ Required properties: - r5g6b5 (16-bit pixels, d[15:11]=r, d[10:5]=g, d[4:0]=b). - a8b8g8r8 (32-bit pixels, d[31:24]=a, d[23:16]=b, d[15:8]=g, d[7:0]=r). +Optional properties: +- clocks : List of clocks used by the framebuffer. Clocks listed here + are expected to already be configured correctly. The OS must + ensure these clocks are not modified or disabled while the + simple framebuffer remains active. +- display : phandle pointing to the primary display hardware node + Example: - framebuffer { +aliases { + display0 = &lcdc0; +} + +chosen { + framebuffer0: framebuffer@1d385000 { compatible = "simple-framebuffer"; reg = <0x1d385000 (1600 * 1200 * 2)>; width = <1600>; height = <1200>; stride = <(1600 * 2)>; format = "r5g6b5"; + clocks = <&ahb_gates 36>, <&ahb_gates 43>, <&ahb_gates 44>; + display = <&lcdc0>; + }; + stdout-path = "display0"; +}; + +soc@01c00000 { + lcdc0: lcdc@1c0c000 { + compatible = "allwinner,sun4i-a10-lcdc"; + ... }; +}; + + +*) Older devicetree files may have a compatible = "simple-framebuffer" node +in a different place, operating systems must first enumerate any compatible +nodes found under chosen and then check for other compatible nodes. |