[PATCH v5 1/2] drm/panel: Add support for Truly NT35597 panel

[Linus Walleij]

On Thu, Aug 9, 2018 at 12:53 PM Thierry Reding <thierry.reding at gmail.com> wrote:

[Me]
> > I suspect this is indeed a panel driver and not a panel with integrated
> > driver. I think the best is to define two compatible strings like
> > we do for ILI9322:
> > "truly,nt35597", "qcom,reference-design-name-display";
>
> I don't understand why we need the two compatible strings for this.
> Having "truly,nt35597" isn't quite correct in that case, because in
> itself that doesn't contain enough information for any programming.
>
> If that chip can indeed be used to drive different panels, what we
> really need is the a compatible string that describes the complete
> assembly. In the driver we could then rely on parameterized common
> code that the panel driver can call into in order to program the
> driver chip.

Good point.

Rob asked the same for the TPO driver, but that case is
different.

For the TPO driver we had a situation where the display driver
was kind of self-identifying, using HW straps to set up the mode,
so the kernel driver only needed to read some registers to
get basic functionality up, so it could use the compatible
of the display driver itself.

In such cases it is useful with two compatible strings as there
are always quirks (that is why we always have two compatible
strings for SoCs) and a specific display/system may need e.g.
specific gamma correction values even if basic graphics come
up with just the display driver compatible strings.

So I would say it depens on how "plug-n-playsy" the display
driver is.

Yours,
Linus Walleij