linux-kernel - Re: [RESEND PATCH v2 3/3] ARM: dts: imx28-cfa10036: Fix the reset gpio signal polarity

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Date:   Tue, 9 Oct 2018 08:29:08 +0000
From:   Vokáč Michal <Michal.Vokac@...ft.com>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Shawn Guo <shawnguo@...nel.org>
CC:     Fabio Estevam <fabio.estevam@....com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>
Subject: Re: [RESEND PATCH v2 3/3] ARM: dts: imx28-cfa10036: Fix the reset
 gpio signal polarity

On 9.10.2018 09:51, Bartlomiej Zolnierkiewicz wrote:
> 
> On 10/09/2018 02:20 AM, Shawn Guo wrote:
>> On Mon, Oct 08, 2018 at 11:45:36AM +0000, Vokáč Michal wrote:
>>> On 27.9.2018 11:24, Michal Vokáč wrote:
>>>> The reset signal of the SSD1306 OLED display is actually active-low.
>>>> Adapt the DT to reflect the real world.
>>>>
>>>> Signed-off-by: Michal Vokáč <michal.vokac@...ft.com>
>>>> ---
>>>> v2 changes: New patch in the series
>>>
>>> Bartlomiej just queued the first two patches for v4.20.
>>> Will somebody take this one? Otherwise this SoM will end up with
>>> broken OLED display reset.
>>
>> Well, it means the change breaks the ABI between kernel and device tree,
>> e.g. the new kernel will not work with existing/installed DTBs.
> 
> Should I revert this sdd10307fb patch then?

Sorry for the inconvenience :( Lesson learned..

So in other words (no offense): broken drivers need to stay broken because
users may already get used to the broken behavior?

Personally I would not describe this change as a device tree ABI change.
It is not a change in the DT binding. Or are "stable device tree API" and
"device tree ABI" really two different things?

The first patch should be OK though.

Michal