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

[Stephen Warren]

On 11/06/2012 12:41 PM, Pantelis Antoniou wrote:
> Hi Russ,
> 
> On Nov 6, 2012, at 8:29 PM, Russ Dill wrote:
> 
>> On Tue, Nov 6, 2012 at 10:35 AM, Tony Lindgren <tony at atomide.com> wrote:
>>> * Grant Likely <grant.likely at secretlab.ca> [121106 03:16]:
>>>> On Tue, Nov 6, 2012 at 10:30 AM, Pantelis Antoniou
>>>> <panto at antoniou-consulting.com> wrote:
>>>>>
>>>>> Another can of worms is the pinctrl nodes.
>>>>
>>>> Yes... new pinctrl data would need to trigger adding new data to
>>>> pinctrl. I don't know if the pinctrl api supports that.
>>>
>>> The actual pins stay the same, just their configuration
>>> changes. AFAIK all that is already supported using the
>>> pinctrl framework.
>>>
>>> For example, considering hotplugging capes on the beaglebone:
...
>> That assumes that for a particular external bus, certain pins aren't
>> already shared with functions already on the board, for instance if an
>> I²C bus brought out to the external bus already has a chip connected
>> to it.
> 
> This is our case on the bone. We don't enable the peripheral until
> a cape that references it is enabled.
> 
> I don't think that very big changes are going to be needed TBH.
...
> Ideally if we could do this in the cape definition:
> 
> 	cape_pinmux {
> 		parent = <&am3358_pinmux>;

I think the cape overlay would simply add nodes to the existing pin
controller node, so I'd presume you would replace the two lines
immediately above with:

am3358_pinmux: pinmux {

> 
>                 bone_dvi_cape_led_pins: pinmux_bone_dvi_cape_led_pins {
>                         pinctrl-single,pins = <
>                                 0x48 0x07       /* gpmc_a2.gpio1_18, OUTPUT | MODE7 */
>                                 0x4c 0x07       /* gpmc_a3.gpio1_19, OUTPUT | MODE7 */
>                         >;
> 	};
> 
>         pinctrl-0 = <&bone_geiger_cape_pins>;