On 11/27/2014 9:56 AM, Leif Lindholm wrote:
> Add a global binding for the chosen node.
> Include a description of the stdout-path, and an explicit statement on
> its extra options in the context of a UART console.
>
> Opening description stolen from www.devicetree.org, and part of the
> remaining text provided by Mark Rutland.
>
> Signed-off-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/chosen.txt | 42 ++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/chosen.txt
>
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> new file mode 100644
> index 0000000..9cd74e9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -0,0 +1,42 @@
> +The chosen node
> +---------------
> +
> +The chosen node does not represent a real device, but serves as a place
> +for passing data between firmware and the operating system, like boot
> +arguments. Data in the chosen node does not represent the hardware.
> +
> +
> +stdout-path property
The code in patch 3/3 adds the extra options feature to the properties:
stdout-path
linux,stdout-path
stdout [if (IS_ENABLED(CONFIG_PPC) ... ]
> +--------------------
> +
> +Device trees may specify the device to be used for boot console output
> +with a stdout-path property under /chosen, as described in ePAPR, e.g.
> +
> +/ {
> + chosen {
> + stdout-path = "/serial@f00:115200";
> + };
> +
> + serial@f00 {
> + compatible = "vendor,some-uart";
> + reg = <0xf00 0x10>;
> + };
> +};
> +
> +If the character ":" is present in the value, this terminates the path.
> +The meaning of any characters following the ":" is device-specific, and
> +must be specified in the relevant binding documentation.
> +
> +For UART devices, the format supported by uart_parse_options() is the
> +expected one. In this case, the format of the string is:
> +
> + <baud>{<parity>{<bits>{<flow>}}}
> +
> +where
> +
> + baud - baud rate in decimal
> + parity - 'n' (none), 'o', (odd) or 'e' (even)
> + bits - number of data bits
> + flow - 'r' (rts)
> +
> +For example: 115200n8r
>
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