linux-kernel - Re: [PATCH] dt: platform: Extract device name from device tree blob

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Date:	Fri, 16 Nov 2012 08:15:36 +0000
From:	"lee.jones@...aro.org" <lee.jones@...aro.org>
To:	Per Förlin <per.forlin@...ricsson.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Fredrik SODERSTEDT <fredrik.soderstedt@...ricsson.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dt: platform: Extract device name from device tree blob

On Thu, 15 Nov 2012, Per Förlin wrote:

> On 11/15/2012 04:52 PM, Grant Likely wrote:
> > On Mon, 12 Nov 2012 23:54:40 +0100, Per FÃ¶rlin <per.forlin@...ricsson.com> wrote:
> >> On 11/12/2012 04:20 PM, Grant Likely wrote:
> >>> On Mon, Nov 12, 2012 at 2:59 PM, Per Forlin <per.forlin@...ricsson.com> wrote:
> >>>> Add support to extract device name from device tree blob.
> >>>> If the property "dev-name" is set in the DTS this name will
> >>>> be used when creating the device.
> >>>> The auxdata_lookup has precedence and will override
> >>>> the "dev-name" property.
> >>>
> >>> Using a 'dev-name' property has the same problem that the 'cell-index'
> >>> properties have in that it is encoding part of the global namespace
> >>> local to the node and it becomes easy to create collisions. Instead of
> >>> this check to see if one of the properties in /aliases points to the
> >>> node and use that for the name.
> >>>
> >>> g.
> >>>
> >> Thanks Grant for your feedback,
> >>
> >> Extract from exynos5250.dtsi:
> >> -----------
> >> 	aliases {
> >> 		spi0 = &spi_0;
> >> 		spi1 = &spi_1;
> >> 		spi2 = &spi_2;
> >> 	};
> >>
> >> 	spi_0: spi@...20000 {
> >> ...
> >> 	};
> >>
> >> 	spi_1: spi@...30000 {
> >> ...
> >> 	};
> >>
> >> 	spi_2: spi@...40000 {
> >> ...
> >> 	};
> >> ---------------
> >>
> >> Alias refers to the device node. The device node is not aware of the alias.
> >>
> >> How to get a device name from the aliases.
> >> 1. Traverse all aliases for each device node (time consuming if there are many aliases)
> >> 2. Make a new function of_alias_get_name(), today there is only of_alias_get_id()
> >> 3. The functionality of setting device_name based on alias name needs to be optional because one may want to use aliases without changing the name of the device.
> >> All this is feasible but perhaps not optimal.
> >>
> >> I don't really see how come name space is a big issue in this case. The name space of "dev-name" is local to the device node. A child device node can use the same dev-name as the parent (unless I'm mistaken which happens quite often). Introducing yet another property name pollutes the name space of the device node. Still I think the pros are stronger than the cons.
> >>
> >> Do you still prefer to use the name of the Alias? Could you please elaborate a bit more how this can be done in practice?
> >> I would agree with you if there was a reference from the device node to the alias.
> > 
> > Oh, I see what you're trying to do. As Lee pointed out you're trying to
> > make the Linux internal way of matching up clocks and regulators happy.
> > That is very much a Linux-kernel internal thing and should be solved in
> > the kernel. Trying to solve it with fixed names in the device tree will
> > cause problems down the road.
> > 
> > I though you were wanting to have logical names for the devices that
> > make sense to the user which is how aliases is used now.
> > 
> > So, no, don't do this.
> > 
> > g.
> > 
> Hi,
> 
> I came to the same conclusion when I dag into it some more. I replied to my own comment and concluded (https://lkml.org/lkml/2012/11/13/309).
> The solution is to move clocks and regulators into the DTS. When this is done there will be no need for setting a specific device-name (all those auxdata_lookup can be removed)

Right, something I will do when we have all the pieces in place.

FWIW, all of the regulators are in the DTS(I) files and are happy.
We're still working on Clocks, I believe Ulf will deal with these.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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