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

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Date:	Tue, 24 May 2016 20:03:48 +0200
From:	Christer Weinigel <christer@...nigel.se>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH] devicetree - document using aliases to set spi bus
 number.


On 05/24/2016 07:20 PM, Mark Brown wrote:
>> 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.
> 
> I'm not sure this is something we want to support at all, I can't 
> immediately see anything that does this deliberately in the SPI
> code and obviously the "bus number" is something of a Linux
> specific concept which would need some explanation if we were going
> to document it.  It's something I'm struggling a bit to see a
> robust use case for that isn't better served by parsing sysfs,
> what's the goal here?

Well, that's how it works right now:

commit bb29785e0d6d150181704be2efcc3141044625e2
Author: Grant Likely <grant.likely@...retlab.ca>
Date:   Fri Dec 21 19:32:09 2012 +0000

    spi/of: Use DT aliases for assigning bus number

> + if ((master->bus_num < 0) && master->dev.of_node) +
> master->bus_num = of_alias_get_id(master->dev.of_node, "spi");

If this isn't something that should be in the Documentation/devicetree
 because it's not generig enough, where should Linux-specific
interpretations such as this be documented?

  /Christer