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

Peter Rosin
2018-04-26T23:09:29Z

On 2018-04-27 00:40, Laurent Pinchart wrote:
> Hi Peter,
>
> Thank you for the patches.
>
> On Friday, 27 April 2018 01:31:15 EEST 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.
>
> I don't think this is the way to go. We have a real lifetime management
> problem with bridges, and device links are just trying to hide the problem
> under the carpet. They will further corner us by making a real fix much more
> difficult to implement. I'll try to comment further in the next few days on
> what I think a better solution would be, but in a nutshell I believe that
> drm_bridge objects need to be refcounted, with a .release() operation to free
> the bridge resources when the reference count drops to zero. This shouldn't be
> difficult to implement and I'm willing to help.

Ok, sp 24/24 is dead, and maybe 23/24 too. But how do you feel about dropping
.of_node in favour of .owner? That gets rid of ugly #ifdefs...

I also have the nagging feeling that .driver_private serves very little real
purpose if there is a .owner so that you can do

dev_get_drvdata(bridge->owner)

for the cases where the container_of macro is not appropriate.

Cheers,
Peter