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

[Simon Glass]

Hi Stephen,

On 29 April 2016 at 10:23, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 04/29/2016 07:23 AM, Simon Glass wrote:
>>
>> Hi Stephen,
>>
>> On 28 April 2016 at 09:55, Stephen Warren <swarren at 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 at 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.

U-Boot does not impose a rule. If you want duplicate device names you
can have them. I think it is bad practice though.

>
> 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.

Anyway I believe my point stands. Whereas users can edit the device
tree and avoid conflicts they cannot do this with auto-probed devices.
So for that case we should have a way of allocating a name before
calling device_bind().

Regards,
Simon