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of: Add bindings for chosen node, stdout-path

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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@linaro.org>
[grant.likely: remove reference to uart_parse_options]
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Grant Likely <grant.likely@linaro.org>
This commit is contained in:
Leif Lindholm 2014-11-27 17:56:05 +00:00 committed by Grant Likely
parent 63ebecc03d
commit 2a9d832cc9
1 changed files with 46 additions and 0 deletions
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46
Documentation/devicetree/bindings/chosen.txt Normal file
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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
--------------------
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 preferred binding is a string in the form:
<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
Implementation note: Linux will look for the property "linux,stdout-path" or
on PowerPC "stdout" if "stdout-path" is not found. However, the
"linux,stdout-path" and "stdout" properties are deprecated. New platforms
should only use the "stdout-path" property.