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 13:07:04 +0200
From:   Marek Vasut <marex@...x.de>
To:     Paulo Pavacic <pavacic.p@...il.com>
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

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.