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

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Message-ID: <CAO9szn0OuKW+-JZMs3TPUHiwLCe6cUPcsUq+og64K2utMyZpqQ@mail.gmail.com>
Date:   Wed, 21 Jun 2023 17:08:57 +0200
From:   Paulo Pavacic <pavacic.p@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     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

pet, 16. lip 2023. u 14:53 Linus Walleij <linus.walleij@...aro.org> napisao je:
>
> On Fri, Jun 16, 2023 at 2:31 PM Paulo Pavacic <pavacic.p@...il.com> wrote:
> > pet, 16. lip 2023. u 13:44 Linus Walleij <linus.walleij@...aro.org> napisao je:
> > >
> > > On Fri, Jun 16, 2023 at 11:57 AM Paulo Pavacic <pavacic.p@...il.com> wrote:
> > > > čet, 15. lip 2023. u 21:55 Linus Walleij <linus.walleij@...aro.org> napisao je:
> > > > >
> > > > > I doubt that the display controller is actually by Fannal, but I guess
> > > > > you tried to find out? We usually try to identify the underlying display
> > > > > controller so the driver can be named after it and reused for more
> > > > > display panels.
> > > >
> > > > Yes, of course, the controller is ST7701S.
> > >
> > > Hm did you try to just refactor
> > > drivers/gpu/drm/panel/panel-sitronix-st7701.c
> > > to support your new panel?
> >
> > Yes I have tried, but there are too many changes needed and I wasn't
> > sure whether I would be breaking compatibility with st7701 based
> > panels.
>
> For the community it creates a problem that now two drivers for similar
> hardware need to be maintained, and that burden will land on the DRM
> maintainers. For this reason it would be better if a joint driver could
> be created.

I will try modifying st7701, but that seems like a big task since
currently st7701 crashes kernel (5.15) for me and I have seen
suggestions to use raydium driver over st7701.
Also I guess I should first read some more documentation and compare
st7701 to st7701s. I currently can't reserve a lot of time for that.

>
> I am sure the users of the old driver will be willing to test patches to
> make sure their devices keep working.

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.

>
> Yours,
> Linus Walleij

Thank you for your time,
Paulo