Re: [PATCH V4 2/3] drm/panel: Add Samsung AMS495QA01 MIPI-DSI LCD panel

["Heiko Stübner" <heiko@sntech.de>]

Hi Linus,

Am Samstag, 3. Dezember 2022, 10:03:42 CET schrieb Linus Walleij:
> On Tue, Nov 29, 2022 at 6:29 PM Chris Morgan <macroalpha82@gmail.com> wrote:
> 
> > From: Chris Morgan <macromorgan@hotmail.com>
> >
> > Support Samsung AMS495QA01 panel as found on the Anbernic RG503. Note
> > This panel receives video signals via DSI, however it receives
> > commands via 3-wire SPI.
> >
> > Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
> > Signed-off-by: Maya Matuszczyk <maccraft123mc@gmail.com>
> 
> > +config DRM_PANEL_SAMSUNG_AMS495QA01
> > +       tristate "Samsung AMS495QA01 DSI panel"
> 
> I am always a bit careful with these "Samsung" panels. Well the
> panel is surely Samsungs and usually it has that name, but very often
> it is mainly a display controller, made by someone else, then a physical
> panel slapped on and then the actual display controller is obscured.
>
> Typical example:
> panel-novatek-nt35560.c handing Samsung ACX424AKP.
> 
> If you know the actual display controller, then the driver should be
> renamed after that, but keeping the compatible and DT bindings
> as is. The reason being that tomorrow there is an LG panel
> using the same display controller and then we don't get duplicate
> code.
> 
> It feels like this is a Novatek controller. Just a feeling I have.
> Mostly from the way it does brightness using ELVSS and
> gamma. But who knows.

Though in past projects I've seen the same display-controller used with
different panels (and different dsi-init-sequences). In one project the
display manufacturer even EOL'ed the first panel and provided a replacement
with said same display controller (and a different init) - but the
datasheets for the display-controller were for the same chip still.

So while in my experience the actual display name from the manufacturer
identifies the display + controller combo, I don't really think you can
go the other way with the controller name identifying the display+controller
combination.

But that whole display business is arcane anyway, so this also only
stems from past projects and not factual knowledge ;-) .


Heiko