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From:   Doug Anderson <dianders@chromium.org>
Date:   Mon, 23 May 2022 16:35:23 -0700
Message-ID: <CAD=FV=Urdfkzz6h4X-5tKvjFaT6eRTNP47s+evkjYaCEfq-Ndg@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: HID: i2c-hid: elan: Introduce
 bindings for Elan eKTH6915
To:     Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc:     "open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Stephen Boyd <swboyd@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>
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Precedence: bulk

Hi,

On Mon, May 23, 2022 at 2:23 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> Like many i2c-hid touchscreen controllers, the Elan eKTH6915
> controller has a reset gpio. For the Goodix GT7375P touchscreen the
> decision was to add a new binding rather than trying to add a new GPIO
> to the existing i2c-hid binding. We'll follow the lead and do it here,
> too.
>
> SIDE NOTE: the Elan eKTH6915 is a touchscreen _controller_ that's
> included as a part on some touchscreens. The reset line isn't truly
> necessary for the functioning of the touchscreen, so it's possible
> that some designs won't have it hooked up and will just guarantee the
> power sequencing requirements with RLC circuits. Thus, we'll mark the
> reset gpio as optional.
>
> Note that if the reset GPIO isn't used there's actually no true need
> to use the "elan,ekth6915" compatible instead of the "hid-over-i2c" on
> Linux. However:
> - Officially using just "hid-over-i2c" for this device violates the
>   existing "hid-over-i2c" bindings. The bindings say that you're not
>   supposed to use "post-power-on-delay-ms" without specifying a more
>   specific compatible. Currently the Linux driver doesn't enforce
>   this, but it violates the bindings to just use
>   "hid-over-i2c". ...and if you're going to add a more specific
>   compatible anyway, might as well do it right.
> - Using this compatible means we don't need to specify
>   "hid-descr-addr" since it's inferred from the compatible.
> - Using this compatible means that the regulator names match the names
>   on the Elan datasheet (vcc33 / vccio) vs the generic hid-over-i2c
>   (vdd / vddl).
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Failure on my part. I should have carried forward from v1:

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>