Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devicesto mach-omap2)

[Cousson, Benoit]

+ Peter

Hi Stephen,

On 11/7/2012 6:25 PM, Stephen Warren wrote:
> On 11/07/2012 03:19 AM, Benoit Cousson wrote:
> > Hi Panto,
> >
> > On 11/07/2012 09:13 AM, Pantelis Antoniou wrote:
> > > Hi Grant
> > >
> > > On Nov 6, 2012, at 9:45 PM, Grant Likely wrote:
> > >
> > > > On Tue, Nov 6, 2012 at 7:34 PM, Pantelis Antoniou
> > > > <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > [ snip ]
> > > > g.
> > >
> > > Since we've started talking about longer term goals, and the versioning
> > > provision seems to stand, I hope we address how much the fragment versioning
> > > thing is similar to the way board revisions progress.
> > >
> > > If a versioning syntax is available then one could create a single DT
> > > file for a bunch of 'almost' similar board and board revisions.
> >
> > I even think that the version issue is probably much more important for the short term than the overlay aspect. Well at least as important. We start having as well a bunch a panda board version with different HW setup.
> >
> > Having a single board-XXX.dts that will support all these versions is probably the best approach to avoid choosing that from the bootloader.
> >
> > We need to figure out a format + mechanism compatible with the current non-versioned format to allow filtering the nodes at runtime to keep only the relevant one.
> >
> > Something that can find the driver that will provide the proper board version or subsystem version or whatever like that:
> >
> > 	compatible-version = "ti,panda-version", "panda";
> >
> > Then at runtime we should create only the node with the correct match between the driver version and the string version.
> >
> >
> > /* regular panda audio routing */
> > sound: sound {
> > 	compatible = "ti,abe-twl6040";
> > 	ti,model = "PandaBoard";
> > 	compatible-version = "ti,panda-version", "panda";
> >
> > 	/* Audio routing */
> > 	ti,audio-routing =
> > 		"Headset Stereophone", "HSOL",
> > 		"Headset Stereophone", "HSOR",
> > 		"Ext Spk", "HFL",
> > 		"Ext Spk", "HFR",
> > 		"Line Out", "AUXL",
> > 		"Line Out", "AUXR",
> > 		"HSMIC", "Headset Mic",
> > 		"Headset Mic", "Headset Mic Bias",
> > 		"AFML", "Line In",
> > 		"AFMR", "Line In";
> > };
> >
> >
> > /* Audio routing is different between PandaBoard4430 and PandaBoardES */
> > &sound {
> > 	ti,model = "PandaBoardES";
> > 	compatible-version = "ti,panda-version", "panda-es";
> >
> > 	/* Audio routing */
> > 	ti,audio-routing =
> > 		"Headset Stereophone", "HSOL",
> > 		"Headset Stereophone", "HSOR",
> > 		"Ext Spk", "HFL",
> > 		"Ext Spk", "HFR",
> > 		"Line Out", "AUXL",
> > 		"Line Out", "AUXR",
> > 		"AFML", "Line In",
> > 		"AFMR", "Line In";
> > };
> >
> >
> > Maybe some extra version match table can just be passed during the board machine_init
> >
> > 	of_platform_populate(NULL, omap_dt_match_table, NULL, NULL, panda_version_match_table);
>
> Is the only difference here the content of the ti,audio-routing
> property? If so, then I don't think there's any need for infra-structure
> for this; the driver code already reads that property and adjusts its
> behaviour based upon it.

That was just an example, and maybe not the best one. It could be any 
kind of HW differences, like a different GPIO line, a different I2C 
peripheral, an extra DCDC...
The point was just that you might have several version of the same node 
with different attributes depending of the board revision.

Regards,
Benoit

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