linux-kernel - [PATCH] Input: ads7846 - don't set ABS

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Message-Id: <20230728133859.3808994-1-bbara93@gmail.com>
Date:   Fri, 28 Jul 2023 15:38:59 +0200
From:   Benjamin Bara <bbara93@...il.com>
To:     dmitry.torokhov@...il.com
Cc:     bbara93@...il.com, benjamin.bara@...data.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Input: ads7846 - don't set ABS_PRESSURE when min == max

Hi Dmitry,

thank you for the feedback!

On Thu, 27 Jul 2023 at 22:39, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> On Thu, Jul 27, 2023 at 05:19:57PM +0200, Benjamin Bara wrote:
> > From: Benjamin Bara <benjamin.bara@...data.com>
> >
> > When the optional fields "pressure_min" and "pressure_max" are not set,
> > both fall back to 0, which results to the following libinput error:
> >
> > ADS7846 Touchscreen: kernel bug: device has min == max on ABS_PRESSURE
> >
> > Avoid it by only setting ABS_PRESSURE if the values differ.
>
> What is the benefit of silently continuing without reporting pressure on
> models that do support pressure readings, vs. using libinput's errors as
> signal to adjust DT?

With the current implementation, libinput rejects the device [1] when an
optional device-tree field is not set, which leads to a "non-functional" device.
But you are right, silently continuing might also not be the best option...
I could provide a v2 where the maximum is set to a fallback value (~0) and a
warning is printed that the pressure is not set and therefore a fallback value
is used, to signal the user to adjust the DT.

What do you think about that?

Best regards
Benjamin

[1] https://gitlab.freedesktop.org/libinput/libinput/-/blob/1.23.0/src/evdev.c?ref_type=tags#L1816