On Wed, Dec 3, 2014 at 2:24 AM, Frank Rowand [off-list ref] wrote:

On 11/27/2014 9:56 AM, Leif Lindholm wrote:

quoted

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 <redacted>
---
 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) ... ]

I don't understand what you mean here. Are you suggesting a change to
this patch? Is there something deficient in it?

g.

quoted

+--------------------
+
+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 at f00:115200";
+     };
+
+     serial at 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