linux-kernel - Re: [PATCH v8 01/11] dt-bindings: display: simple: List hpd properties in panel-simple

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Date:   Wed, 2 Jun 2021 13:00:17 -0500
From:   Rob Herring <robh@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        robdclark@...omium.org, Andrzej Hajda <a.hajda@...sung.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Steev Klimaszewski <steev@...i.org>,
        Sam Ravnborg <sam@...nborg.org>, linux-arm-msm@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Linus W <linus.walleij@...aro.org>,
        Jonas Karlman <jonas@...boo.se>, Lyude Paul <lyude@...hat.com>,
        Thierry Reding <treding@...dia.com>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v8 01/11] dt-bindings: display: simple: List hpd
 properties in panel-simple

On Mon, 24 May 2021 17:01:49 -0700, Douglas Anderson wrote:
> The HPD (Hot Plug Detect) signal is present in many (probably even
> "most") eDP panels. For eDP, this signal isn't actually used for
> detecting hot-plugs of the panel but is more akin to a "panel ready"
> signal. After you provide power to the panel, panel timing diagrams
> typically say that you should wait for HPD to be asserted (or wait a
> fixed amount of time) before talking to the panel.
> 
> The panel-simple bindings describes many eDP panels and many of these
> panels provide the HPD signal. We should add the HPD-related
> properties to the panel-simple bindings. The HPD properties are
> actually defined in panel-common.yaml, so adding them here just
> documents that they are OK for panels handled by the panel-simple
> bindings.
> 
> NOTE: whether or not we'd include HPD properties in the panel node is
> more a property of the board design than the panel itself. For most
> boards using these eDP panels everything "magically" works without
> specifying any HPD properties and that's been why we haven't needed to
> allow the HPD properties earlier. On these boards the HPD signal goes
> directly to a dedicated "HPD" input to the eDP controller and this
> connection doesn't need to be described in the device tree. The only
> time the HPD properties are needed in the device tree are if HPD is
> hooked up to a GPIO or if HPD is normally on the panel but isn't used
> on a given board. That means that if we don't allow the HPD properties
> in panel-simple then one could argue that we've got to boot all eDP
> panels (or at least all those that someone could conceivably put on a
> system where HPD goes to a GPIO or isn't hooked up) from panel-simple.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
> Changes in v8:
> - Explain better why HPD needs to be in panel-simple in commit msg.
> 
> Changes in v7:
> - List hpd properties bindings patch new for v7.
> 
>  .../devicetree/bindings/display/panel/panel-simple.yaml         | 2 ++
>  1 file changed, 2 insertions(+)
> 

Reviewed-by: Rob Herring <robh@...nel.org>