92 lines
3.6 KiB
Plaintext
92 lines
3.6 KiB
Plaintext
Simple Framebuffer
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A simple frame-buffer describes a frame-buffer setup by firmware or
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the bootloader, with the assumption that the display hardware has already
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been set up to scan out from the memory pointed to by the reg property.
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Since simplefb nodes represent runtime information they must be sub-nodes of
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the chosen node (*). Simplefb nodes must be named "framebuffer@<address>".
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If the devicetree contains nodes for the display hardware used by a simplefb,
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then the simplefb node must contain a property called "display", which
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contains a phandle pointing to the primary display hw node, so that the OS
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knows which simplefb to disable when handing over control to a driver for the
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real hardware. The bindings for the hw nodes must specify which node is
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considered the primary node.
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It is advised to add display# aliases to help the OS determine how to number
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things. If display# aliases are used, then if the simplefb node contains a
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"display" property then the /aliases/display# path must point to the display
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hw node the "display" property points to, otherwise it must point directly
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to the simplefb node.
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If a simplefb node represents the preferred console for user interaction,
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then the chosen node's stdout-path property should point to it, or to the
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primary display hw node, as with display# aliases. If display aliases are
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used then it should be set to the alias instead.
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It is advised that devicetree files contain pre-filled, disabled framebuffer
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nodes, so that the firmware only needs to update the mode information and
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enable them. This way if e.g. later on support for more display clocks get
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added, the simplefb nodes will already contain this info and the firmware
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does not need to be updated.
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If pre-filled framebuffer nodes are used, the firmware may need extra
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information to find the right node. In that case an extra platform specific
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compatible and platform specific properties should be used and documented,
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see e.g. simple-framebuffer-sunxi.txt .
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Required properties:
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- compatible: "simple-framebuffer"
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- reg: Should contain the location and size of the framebuffer memory.
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- width: The width of the framebuffer in pixels.
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- height: The height of the framebuffer in pixels.
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- stride: The number of bytes in each line of the framebuffer.
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- format: The format of the framebuffer surface. Valid values are:
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- r5g6b5 (16-bit pixels, d[15:11]=r, d[10:5]=g, d[4:0]=b).
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- a8b8g8r8 (32-bit pixels, d[31:24]=a, d[23:16]=b, d[15:8]=g, d[7:0]=r).
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Optional properties:
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- clocks : List of clocks used by the framebuffer.
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- *-supply : Any number of regulators used by the framebuffer. These should
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be named according to the names in the device's design.
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The above resources are expected to already be configured correctly.
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The OS must ensure they are not modified or disabled while the simple
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framebuffer remains active.
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- display : phandle pointing to the primary display hardware node
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Example:
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aliases {
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display0 = &lcdc0;
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}
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chosen {
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framebuffer0: framebuffer@1d385000 {
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compatible = "simple-framebuffer";
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reg = <0x1d385000 (1600 * 1200 * 2)>;
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width = <1600>;
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height = <1200>;
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stride = <(1600 * 2)>;
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format = "r5g6b5";
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clocks = <&ahb_gates 36>, <&ahb_gates 43>, <&ahb_gates 44>;
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lcd-supply = <®_dc1sw>;
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display = <&lcdc0>;
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};
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stdout-path = "display0";
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};
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soc@1c00000 {
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lcdc0: lcdc@1c0c000 {
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compatible = "allwinner,sun4i-a10-lcdc";
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...
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};
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};
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*) Older devicetree files may have a compatible = "simple-framebuffer" node
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in a different place, operating systems must first enumerate any compatible
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nodes found under chosen and then check for other compatible nodes.
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