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

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Message-ID: <CAO9szn1QdB5WGshuyCOGqb0qbBWHqoikeiMkk+bNGhAF5TX5ew@mail.gmail.com>
Date:   Wed, 12 Jul 2023 14:07:10 +0200
From:   Paulo Pavacic <pavacic.p@...il.com>
To:     Marek Vasut <marex@...x.de>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Maya Matuszczyk <maccraft123mc@...il.com>,
        neil.armstrong@...aro.org, sam@...nborg.org, airlied@...il.com,
        daniel@...ll.ch, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 3/3] drm/panel-fannal-c3004: Add fannal c3004 DSI panel

Hello all,

sub, 8. srp 2023. u 14:53 Marek Vasut <marex@...x.de> napisao je:
>
> On 7/7/23 17:26, Paulo Pavacic wrote:
> > Hello Marek,
>
> Hi,
>
> > čet, 6. srp 2023. u 17:26 Marek Vasut <marex@...x.de> napisao je:
> >>
> >> On 7/6/23 17:18, Paulo Pavacic wrote:
> >>> Hello Linus,
> >>>
> >>> čet, 22. lip 2023. u 10:22 Linus Walleij <linus.walleij@...aro.org> napisao je:
> >>>>
> >>>> On Wed, Jun 21, 2023 at 5:09 PM Paulo Pavacic <pavacic.p@...il.com> 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.

I would like to create new driver because panel-st7701 seems to be
outdated and is using non-standard macro (ST7701_WRITE()) and for me
it is crashing kernel 5.15.
Does anyone have similar issues with it?

Br,
Paulo