Re: [PATCH RESEND v2 08/12] dt-bindings: add binding for generic eDP panel

From: Rob Herring <robh+dt@kernel.org>
To: Vasily Khoruzhick <anarsoul@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree <devicetree@vger.kernel.org>,
	David Airlie <airlied@linux.ie>,
	linux-sunxi <linux-sunxi@googlegroups.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Chen-Yu Tsai <wens@csie.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Sean Paul <seanpaul@chromium.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	arm-linux <linux-arm-kernel@lists.infradead.org>,
	Icenowy Zheng <icenowy@aosc.io>
Subject: Re: [PATCH RESEND v2 08/12] dt-bindings: add binding for generic eDP panel
Date: Mon, 4 Feb 2019 10:39:08 -0600	[thread overview]
Message-ID: <CAL_JsqLAODca_U94hCi9O3E6XiUjAYCoL7_0gkf_eMY0nnT8Ag@mail.gmail.com> (raw)
In-Reply-To: <CA+E=qVew+8__yrAud1gFnLQ8HCwDdGhVjV=c173HGvZxH=7zZQ@mail.gmail.com>

On Mon, Feb 4, 2019 at 10:11 AM Vasily Khoruzhick <anarsoul@gmail.com> wrote:
>
> On Mon, Feb 4, 2019 at 12:24 AM Thierry Reding <thierry.reding@gmail.com> wrote:
> > >
> > > Pinebook used several 768p panels that have slightly different timings
> > > and recent batch uses 1080p panel.
> > >
> > > What panel descriptor should I use as fallback?
> >
> > You don't use panel descriptors as fallback. The simple-panel driver
> > will bind to a panel device and use the corresponding descriptor. If
> > your device tree contains the correct information, the descriptor is
> > correct for the panel you have.
> >
> > In other words you need to ensure that you have the correct panel in
> > device tree for the board that you're using. This is exactly the same
> > thing as for other devices.
> >
> > One way to to this is to have separate device trees for each variant
> > of the board that you want to support. Another variant may be to have
> > a common device tree and then have some early firmware update the DTB
> > with the correct panel information.
>
> That defeats the purpose of using eDP panels. Panel can identify
> itself and report what timings it supports.

If you are confident that this works for all panels, then the firmware
can identify the right panel and update the DTB with the correct
information. If this doesn't work in the firmware, then it is not
going to work in the kernel either and you are SOL without specific
panel information in the DT.

> If we use separate DTBs then users will have to figure out what panel
> is installed in their hardware and use appropriate software image -
> that's something I'd like to avoid.

I think Thierry meant either way this is a firmware problem. If you
have a SKU per device and panel type, then the firmware just picks a
dtb among a set.

Rob
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