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

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Date:   Sat, 8 Jul 2023 09:11:02 +0200 (GMT+02:00)
From:   Paulo Pavačić <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 Marek,


Jul 6, 2023 5:26:15 PM Marek Vasut <marex@...x.de>:

> 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 them, but there are some.

So far I can see that default register values are different, previously unused registers are now used and there has been some reordering of how info is placed in registers [1] (return value for some commands is different). E.g AJ1N[1:0] has been moved from B102h to B101h [1]

Moreover, instructions to some commands have been changed as well as 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:
[1] https://ibb.co/NmgbZmy - GAMACTRL_st7701.png
[2] https://ibb.co/G79y235 - PCLKS2.png

P.S. this is second time I'm trying to send this e-mail so some of you might have received e-mail with the same text twice


Thank you for your time,
Paulo