Re: [PATCH 00/24] device link, bridge supplier <-> drm device

Peter Rosin
2018-04-27T07:52:01Z

On 2018-04-27 09:37, Peter Rosin wrote:
> On 2018-04-27 09:11, Andrzej Hajda wrote:
>> Hi Peter,
>>
>> On 27.04.2018 00:31, Peter Rosin wrote:
>>> Hi!
>>>
>>> It was noted by Russel King [1] that bridges (not using components)
>>> might disappear unexpectedly if the owner of the bridge was unbound.
>>> Jyri Sarha had previously noted the same thing with panels [2]. Jyri
>>> came up with using device links to resolve the panel issue, which
>>> was also my (independent) reaction to the note from Russel.
>>>
>>> This series builds up to the addition of that link in the last
>>> patch, but in my opinion the other 23 patches do have merit on their
>>> own.
>>>
>>> The last patch needs testing, while the others look trivial. That
>>> said, I might have missed some subtlety.
>>
>> of_node is used as an identifier of the bridge in the kernel. If you
>> replace it with device pointer there will be potential problem with
>> devices having two or more bridges, how do you differentiate bridges if
>> the owner is the same? If I remember correctly current bridge code does
>> not allow to have multiple bridges in one device, but that should be
>> quite easy to fix if necessary. After this change it will become more
>> difficult.
>
> I don't see how it will be more difficult?
>
>> Anyway I remember discussion that in DT world bridge should be
>> identified rather by of_graph port node, not by parent node as it is
>> now. If you want to translate this relation to device owner, you should
>> add also port number to have full identification of the bridge, ie pair
>> (owner, port_number) would be equivalent of port node.
>
> You even state the trivial solution here, just add the port/endpoint ID
> when/if it is needed. So, what is the significant difference?

Or, since this is apparently a rare requirement, you could make the owners
that do need it fix it themselves. E.g. by embedding the struct drm_bridge
in another struct that contains the needed ID, and use container_of to get
to that containing struct with the ID.

Cheers,
Peter