[U-Boot] [RFC PATCH] dm: ensure device names are unique

[Stephen Warren <swarren@wwwdotorg.org>]

On 04/29/2016 07:23 AM, Simon Glass wrote:
> Hi Stephen,
>
> On 28 April 2016 at 09:55, Stephen Warren <swarren@wwwdotorg.org> wrote:
>> On 04/27/2016 10:50 PM, Simon Glass wrote:
>>>
>>> Hi Stephen,
>>>
>>> On 26 April 2016 at 15:30, Stephen Warren wrote:
>>>   > It is possible for HW to contain multiple instances of the same device.
>>> In
>>>   > this case, the name passed to device_bind() may not be unique across
>>> all
>>>   > devices within its uclass. One example is a system with multiple
>>> identical
>>>   > PCI Ethernet devices. Another might be a system with multiple identical
>>>   > I2C GPIO expanders, each connected to a separate I2C bus, yet using the
>>>   > same I2C address on that bus and hence having the same DT node name.
>>>   >
>>>   > Enhance the code to detect this situation, and append a sequence
>>> number so
>>>   > the device name to ensure uniqueness.
>>>   >
>>>   > Signed-off-by: Stephen Warren <swarren at nvidia.com <swarren@nvidia.com>>
>>>
>>> I would rather that the caller handles this. But failing this perhaps a
>>> new function that does it? Is this for the Ethernet use case?
>>
>>
>> Wouldn't all callers of this function simply call the new function? I'm not
>> aware of any case where the code to avoid duplicate names would not be
>> desired.
>>
>> I hit this for the Ethernet case, but I believe it applies to any type of
>> device at all; see another possible trigger case in the commit description.
>
> This does not happen with devices from the device tree. It only
> happens with auto-probed devices. Your I2C GPIO example is odd but I'd
> rather solve that by using the device tree node name.

DT itself imposes no such rule; node names must be unique only within 
their parent node but there's no restriction on identical node names 
appearing in different parts of the tree.

If U-Boot imposes that rule on DT, then there's no way in general that 
we can guarantee U-Boot will be able to use standard DTs (i.e. identical 
to those used by Linux or any other OS) for any platform; it'd be 
another change someone would need to make to transform a DT to be 
"U-Boot compatible", which rather reduces a potential benefit of DT for 
U-Boot; being able to just drop a DT in and have it work.

It would be possible for U-Boot to decouple its internal device name 
from the DT node name. In which case, your statement would work. 
However, I don't think that's the case at the moment, and in fact it's 
effectively what this patch is doing, although admittedly there are 
other ways of doing this.