Re: [PATCH] devicetree - document using aliases to set spi bus number.

From: Frank Rowand <frowand.list@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Christer Weinigel <christer@weinigel.se>,
	linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
	devicetree@vger.kernel.org, Mark Brown <broonie@kernel.org>
Subject: Re: [PATCH] devicetree - document using aliases to set spi bus number.
Date: Wed, 25 May 2016 08:25:44 -0700	[thread overview]
Message-ID: <5745C3F8.4020909@gmail.com> (raw)
In-Reply-To: <20160524174140.GE11605@leverpostej>

On 5/24/2016 10:41 AM, Mark Rutland wrote:
> On Tue, May 24, 2016 at 06:39:20PM +0200, Christer Weinigel wrote:
>> Document how to use devicetree aliases to assign a stable
>> bus number to a spi bus.
>>
>> Signed-off-by: Christer Weinigel <christer@weinigel.se>
>>
>> ---
>>
>> Trivial documentation change.
>>
>> Not having used devicetree that much it was surprisingly hard to
>> figure out how to assign a stable bus number to a spi bus.  Add a
>> simple example that shows how to do that.
>>
>> Mark Cced as the SPI maintainer.  Or should trivial documentation
>> fixes like this be addressed to someone else?
>>
>>   /Christer
>>
>>  Documentation/devicetree/bindings/spi/spi-bus.txt | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> index 42d5954..c35c4c2 100644
>> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
>> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> @@ -94,3 +94,13 @@ SPI example for an MPC5200 SPI bus:
>>  			reg = <1>;
>>  		};
>>  	};
>> +
>> +Normally SPI buses are assigned dynamic bus numbers starting at 32766
>> +and counting downwards.  It is possible to assign the bus number
>> +statically using devicetee aliases.  For example, on the MPC5200 the
>> +"spi@f00" device above is connected to the "soc" bus.  To set its
>> +bus_num to 1 add an aliases entry like this:
> 
> As Mark Brown pointed out, this is very Linux-specific (at least in the
> wording of the above).
> 
> Generally, aliases are there to match _physical_ identifiers (e.g. to
> match physical labels for UART0, UART1, and on).

Can you point to anything in the specification or any other place that
states that aliases are for matching physical identifiers?

Can you point to anything in the specification or any other place that
states that aliases are not to be used for anything else?

> 
> I'm not sure whether that applies here.
> 
> Thanks,
> Mark.
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