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

[Benoit Cousson]

On 11/07/2012 12:02 PM, Pantelis Antoniou wrote:
> Hi Benoit,
> 
> On Nov 7, 2012, at 11:19 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 at antoniou-consulting.com> 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.
>>
>>
> 
> This is exactly what we need. FWIW the capebus syntax is a little bit different.
> 
>> /* 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";
>> };
>>
> 
> We use this syntax for capebus (totally non-standard of-course),
> 
> sound: sound {
> 	compatible = "ti,abe-twl6040";
> 	
> 
> 	model at 0 {
> 		ti,model = "PandaBoard";
> 		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";
> 	};
> 
> 	model at 1 {
> 		ti,model = "PandaBoardES";
> 		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";
> 	};
> 
> 	/* common properties for either model */
> };
> 
> The difference is that you don't get to repeat the common properties.
> 
> I don't know if this breaks any conventions but seems to work fine for our case.

Yeah, my main concern with that approach is that you change the
structure of the tree by adding an extra node/hierarchy that will not be
there in case of non-versioned tree.
That's why I think we should have something lighter that will not change
the structure.
Ideally we should be able to add extra versioned node to the original
dts without changing it at all.

>> 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);
>>
> 
> Would we need explicit of_platform_populate calls if we have node modification notifiers?
> In that case the notifier would pick it up automatically, and can do the per
> version matching internally.

Yes indeed, but here I was thinking about an intermediate step, i.e.
now, without any dynamic node insertion mechanism.
Thanks to this simple approach, when can already fix the board
versionning problem.

Regards,
Benoit