Re: [PATCH v4 3/3] drm/panel-fannal-c3004: Add fannal c3004 DSI panel

[Marek Vasut]

On 7/7/23 17:26, Paulo Pavacic wrote:
> Hello Marek,

Hi,

> čet, 6. srp 2023. u 17:26 Marek Vasut <marex@xxxxxxx> napisao je:
> > On 7/6/23 17:18, Paulo Pavacic wrote:
> > > Hello Linus,
> > >
> > > čet, 22. lip 2023. u 10:22 Linus Walleij <linus.walleij@xxxxxxxxxx> napisao je:
> > > > On Wed, Jun 21, 2023 at 5:09 PM Paulo Pavacic <pavacic.p@xxxxxxxxx> wrote:
> > > >
> > > > > A lot of modifications to st7701 are required. I believe it would
> > > > > result in a driver that doesn't look or work the same. e.g compare
> > > > > delays between initialization sequences of panel-fannal-c3004 and
> > > > > panel-st7701. I think it would be optimal to create st7701s driver and
> > > > > have special handling for st7701s panels. If there was a flag for
> > > > > whether panel is st7701 or st7701s it would end up looking like a
> > > > > mess.
> > > >
> > > > What matters is if the original authors of the old st7701 driver are
> > > > around and reviewing and testing patches at all. What we need is
> > > > active maintainers. (Added Jagan, Marek & Maya).
> > > >
> > > > I buy the reasoning that the st7701s is perhaps substantially different
> > > > from st7701.
> > > >
> > > > If st7701s is very different then I suppose it needs a separate driver,
> > > > then all we need to to name the driver properly, i.e.
> > > > panel-sitronix-st7701s.c.
> > >
> > > I had in person talk with Paul Kocialkowski and I have concluded that
> > > this is the best solution.
> > > I believe I should rename it to st7701s due to the hardware changes. I
> > > would like to create V5 patch with driver renamed to st7701s.
> > > Please let me know if you agree / disagree.
> >
> > If I recall it right, the ST7701 and ST7701S are basically the same
> > chip, aren't they ?
>
> I'm currently exploring all the differences. There aren't a lot of
> differences, but there are some.
> So far I can see that default register values are different, new
> previously unused registers are now used and there has been some
> reordering of how info is placed in registers [1] (data bits are in
> different order). Moreover, instructions to some commands have been
> changed and meaning of what data bits mean [2][3]. Also, new features
> have been added [2]; there is now PCLKS 3 for example.
>
> You can see few differences in following images. Same images were
> attached in this mail:
> [1] https://ibb.co/NmgbZmy - GAMACTRL_st7701.png
> [2] https://ibb.co/G79y235 - PCLKS2.png

Ouch. I wonder if this is still something that can be abstracted out 
with some helper accessor functions like:

if (model == ST7701)
  write something
else
  write the other layout

Or whether it makes sense to outright have a separate driver. The later 
would introduce duplication, but maybe that much duplication is OK.