[PATCH] of: Add a reg-names property to name reg entries

[Segher Boessenkool]

>>>> What problem does any of this solve?  The device binding for the
>>>> "mcasp" device will have to describe the possible "reg-names", and
>>>> what those mean; but the binding already has to describe its "reg"
>>>> property anyway.
>>>
>>> What this solve is the ability to use the
>>> platform_get_resource_byname directly to retrieve the proper
>>> register base address.
>>
>> You do not have to put it in the device tree for that, the device
>> driver can implement this itself if it cares.
>
> ???
>
> The driver is the user of that name, so it has to be populated  
> before into the resource during device creation.

It can be as simple as

#define FOO_REG_INDEX 0
#define BAR_REG_INDEX 1

but you can use C strings if you want to.

>>> The binding is just a text description that the driver will not be
>>> able to use directly. It will have to get the resource using an
>>> abstract index.
>>
>> Your reg-names are abstract identifiers just as well.
>
> This is the name used in the HW documentation.

So?  The device binding will still have to list them, for exact spelling
and register block size etc.

> Ordering them to get a number is purely arbitrary.

Ordering them is required, "reg" is an array.  It also matters which
entry is the first entry (for the unit address).

> That's why using the name will allow the driver to get the resource  
> the way it is represented in the documentation and thus avoid some  
> intermediate number.

You use an intermediate string instead, and add code and binding to
translate that to that same number.

>>> It thus removes a level of indirection that is error prone and
>>> useless most of the time.
>>
>> It *adds* a level of indirection.  I doubt it helps prevent errors
>> either, but who knows.
>
> Well, if that does not bring anything to you, you can just not use it.

I could, if you did this for your device binding only, but it seems
you are adding this as a generic thing.  I am very much against that.
The device tree should describe the hardware; it shouldn't describe
the description of the hardware, that's what bindings are for.


Segher