linux-kernel - Re: [PATCH 2/2] Revert "drm: of: Lookup if child node has panel or bridge"

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Message-ID: <CAMty3ZAw7DUSnBePC05qC8Gn6ESKiu+FHw4a-HPPc05VX1hqhg@mail.gmail.com>
Date:   Thu, 21 Apr 2022 13:15:54 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Rob Clark <robdclark@...il.com>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Robert Foss <robert.foss@...aro.org>
Subject: Re: [PATCH 2/2] Revert "drm: of: Lookup if child node has panel or bridge"

+ Linus
+ Marek
+ Laurent
+ Robert

On Thu, Apr 21, 2022 at 4:40 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> Commit '80253168dbfd ("drm: of: Lookup if child node has panel or
> bridge")' attempted to simplify the case of expressing a simple panel
> under a DSI controller, by assuming that the first non-graph child node
> was a panel or bridge.
>
> Unfortunately for non-trivial cases the first child node might not be a
> panel or bridge.  Examples of this can be a aux-bus in the case of
> DisplayPort, or an opp-table represented before the panel node.
>
> In these cases the reverted commit prevents the caller from ever finding
> a reference to the panel.
>
> This reverts commit '80253168dbfd ("drm: of: Lookup if child node has
> panel or bridge")', in favor of using an explicit graph reference to the
> panel in the trivial case as well.

This eventually breaks many child-based devm_drm_of_get_bridge
switched drivers.  Do you have any suggestions on how to proceed to
succeed in those use cases as well?

Jagan.