linux-kernel - Re: [PATCH v3 1/3] devicetree: of: Add bindings for chosen node, stdout-path

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Date:	Tue, 02 Dec 2014 18:24:21 -0800
From:	Frank Rowand <frowand.list@...il.com>
To:	Leif Lindholm <leif.lindholm@...aro.org>
CC:	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, mark.rutland@....com, andrew@...n.ch,
	s.hauer@...gutronix.de, robh+dt@...nel.org, ijc@...ian.org,
	grant.likely@...aro.org, plagnioj@...osoft.com,
	frowand.list@...il.com
Subject: Re: [PATCH v3 1/3] devicetree: of: Add bindings for chosen node,
 stdout-path

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@...aro.org>
> ---
>  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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