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

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Date:	Wed, 25 May 2016 17:06:33 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Frank Rowand <frowand.list@...il.com>
Cc:	Christer Weinigel <christer@...nigel.se>,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] devicetree - document using aliases to set spi bus
 number.

On Wed, May 25, 2016 at 08:25:44AM -0700, Frank Rowand wrote:
> On 5/24/2016 10:41 AM, Mark Rutland wrote:
> > On Tue, May 24, 2016 at 06:39:20PM +0200, Christer Weinigel wrote:
> >> +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?

You have me there; I cannot find any wording to that effect, and I am
evidently going by my understanding alone.

IEEE 1275 simply states that there may be predefined aliases for a
machine, or that users can create and use them dynamically. ePAPR (and
the devicetree specification) only states that aliases exist, and that a
client program might use them (through some means which is never
described).

Thanks,
Mark.