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

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Date:	Wed, 3 Dec 2014 15:12:03 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Frank Rowand <frowand.list@...il.com>
Cc:	Leif Lindholm <leif.lindholm@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Andrew Lunn <andrew@...n.ch>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	Rob Herring <robh+dt@...nel.org>,
	Ian Campbell <ijc@...ian.org>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
Subject: Re: [PATCH v3 1/3] devicetree: of: Add bindings for chosen node, stdout-path

On Wed, Dec 3, 2014 at 2:24 AM, Frank Rowand <frowand.list@...il.com> wrote:
> 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) ... ]

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

g.

>
>> +--------------------
>> +
>> +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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