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

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Message-ID: <7d4bceeb-9611-cbf9-3906-fef5db88aad8@axentia.se>
Date:   Fri, 27 Apr 2018 09:37:11 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Andrzej Hajda <a.hajda@...sung.com>, linux-kernel@...r.kernel.org
Cc:     Archit Taneja <architt@...eaurora.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Martin Donnelly <martin.donnelly@...com>,
        Martyn Welch <martyn.welch@...labora.co.uk>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Clark <robdclark@...il.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Vincent Abriou <vincent.abriou@...com>,
        Jyri Sarha <jsarha@...com>, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH 00/24] device link, bridge supplier <-> drm device

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?

Cheers,
Peter