forked from Minki/linux
bd58a39080
The physical display tied to the framebuffer may have regulators providing power to it, such as power for LCDs or interface conversion chips. The number of regulators in use may vary, but the regulator supply binding can not be a list. Instead just support any named regulator supply properties under the device node. These should be properly named to match the device schematics / design. The driver should take care to go through them all. Signed-off-by: Chen-Yu Tsai <wens@csie.org> Reviewed-by: Hans de Goede <hdegoede@redhat.com> Acked-by: Mark Brown <broonie@kernel.org> Acked-by: Rob Herring <robh@kernel.org> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
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@01c00000 {
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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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