Subject: How to handle named resources with DT?

From: [email-masked] (Cousson, Benoit)
Date: Tue, 9 Aug 2011 23:53:32 +0200

On 8/9/2011 11:49 PM, Grant Likely wrote:
> On Tue, Aug 09, 2011 at 11:44:35PM +0200, Cousson, Benoit wrote:
>> On 8/9/2011 11:17 PM, Grant Likely wrote:
>>> On Tue, Aug 09, 2011 at 11:08:09PM +0200, Cousson, Benoit wrote:
>>>> On 8/9/2011 10:57 PM, Grant Likely wrote:
>>>>> On Tue, Aug 09, 2011 at 01:26:29PM -0500, Scott Wood wrote:
>>>>>> On 08/09/2011 12:47 PM, Cousson, Benoit wrote:
>>>>>>> On 8/9/2011 7:23 PM, Grant Likely wrote:
>>>>>>>> There is no analogous mechanism for _byname in the device tree.  The
>>>>>>>> DT binding for a device must explicitly state what order the register
>>>>>>>> ranges are in.  The driver will need to be adapted.
>>>>>>>
>>>>>>> That seems to be a small regression for my point of view. Relying on the
>>>>>>> order is not super safe. This is not very readable either. That's for
>>>>>>> that exact reason that we changed our drivers to use
>>>>>>> platform_get_resource_byname. That's probably the reason why that API is
>>>>>>> there as well.
>>>>>>> For the same IP, the number of entries can vary depending of the SoC
>>>>>>> revision.
>>>>>>> By using the _byname, we can check if the resource is there or not
>>>>>>> without having to care about the position.
>>>>>>
>>>>>> You could have a named u32 property that contains the reg index, e.g.:
>>>>>>
>>>>>> dev {
>>>>>> 	reg =<0x20000 0x200 0x24000 0x200>;
>>>>>> 	foo-reg =<0>;
>>>>>> 	bar-reg =<1>;
>>>>>> };
>>>>>
>>>>> That's a little nasty.  A reg-names = "foo", "bar"; would probably be
>>>>> better.
>>>>
>>>> Yep, I agree.
>>>>
>>>> And what about something like that?
>>>>    reg =<0x20000 0x200>, "foo",
>>>> 	<0x20000 0x200>, "bar" ;
>>>>
>>>> It is doable?
>>>
>>> Definitely not.  It would break all existing 'reg' parsing
>>> implementations quite badly.
>>
>> OK, so what about extending the reg attribute to be a reg node?
>>
>> dev {
>> 	reg {
>> 		name = "foo_wrapper";
>> 		start =<0x10000>;
>> 		end =<0x200>;
>> 	}
>> 	reg {
>> 		name = "foo";
>> 		start =<0x20000>;
>> 		end =<0x200>;
>> 	}
>> }
>>
>> A little bit more verbose, but at least we can add any attribute we want.
>
> That won't work either because that also breaks the existing 'reg'
> binding.  Anything you do will need to supplement the existing
> binding without changing it in an incompatible way.

OK, but can we add a new attribute then? reg2, reg_ng, reg_plusplus, 
reg_named...?

Benoit