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

From: Rob Herring <robh@kernel.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>,
	David Airlie <airlied@linux.ie>,
	Thierry Reding <thierry.reding@gmail.com>,
	robdclark@chromium.org, Andrzej Hajda <a.hajda@samsung.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-kernel@vger.kernel.org,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Steev Klimaszewski <steev@kali.org>,
	Sam Ravnborg <sam@ravnborg.org>,
	linux-arm-msm@vger.kernel.org,
	Neil Armstrong <narmstrong@baylibre.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	Linus W <linus.walleij@linaro.org>,
	Jonas Karlman <jonas@kwiboo.se>, Lyude Paul <lyude@redhat.com>,
	Thierry Reding <treding@nvidia.com>,
	Stephen Boyd <swboyd@chromium.org>
Subject: Re: [PATCH v8 01/11] dt-bindings: display: simple: List hpd properties in panel-simple
Date: Wed, 2 Jun 2021 13:00:17 -0500	[thread overview]
Message-ID: <20210602180017.GA3674744@robh.at.kernel.org> (raw)
In-Reply-To: <20210524165920.v8.1.Ieb731d23680db4700cc41fe51ccc73ba0b785fb7@changeid>

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@chromium.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@kernel.org>