[PATCH 1/2] drm/panel: Augment the TPO TPG110 bindings

[Linus Walleij]

On Wed, Jun 27, 2018 at 7:21 PM Rob Herring <robh at kernel.org> wrote:
> On Thu, Jun 21, 2018 at 08:49:41PM +0200, Linus Walleij wrote:

> > +This panel driver can driver a variety of panels. It requires
>
> s/can driver/can drive/
>
> Though what a driver supports is irrelevant to the binding...

It it not a software driver the text is referring to. It is a
electrical interface to a panel. Like how a TTL circuit connected
to a LED is referred to as a "LED driver", it's simply what the
industry calls these things.

So there are two things: the panel driver and the panel, the
same panel driver is used with several panels. What the
electronics engineer will do is put a panel driver like this
into his design and then connect some panel s/he finds
in the right quantity in the streets of Shenzhen.

> If you remove timings, how does it drive a variety of panels? Just by
> compatible?

Yes.

Like we did for
Documentation/devicetree/bindings/display/panel/ilitek,ili9322.txt
which is similar to this.

In fact I think many panel drivers are just sloppily slipping in
under the radar as "panels" in our bindings.

>That would mean "tpo,tpg110" alone is not valid nor useful
> as a fallback.

Actually it is. The hardware is wired up to the desired
resolution with hardware straps, which appear in
the registers the (software) driver can read out so
this is ideally self-describing hardware.

But for the event that something needs tweaking in the
future, like we overspecify say SoCs, I include the
exact system on which it is deployd as a separate
compatible string.

> > +a few GPIO lines for control of its reset line and custom serial
> > +protocol.
> >
> >  Required properties:
> > -- compatible : "tpo,tpg110"
> > +- compatible : one of:
> > +  "ste,nomadik-nhk15-display", "tpo,tpg110"
> > +  "tpo,tpg110"
> >  - grestb-gpios : panel reset GPIO
> >  - scen-gpios : serial control enable GPIO
> >  - scl-gpios : serial control clock line GPIO
> >  - sda-gpios : serial control data line GPIO
>
> I2C? That should be done differently...

It is not I2C, the lines are just named confusingly
similar. None of the I2C (-like) protocols apply.
I was similarly confused when I first implemented it.

(Maybe I should add a comment to explain this.)

Yours,
Linus Walleij