linux-kernel - Re: [PATCH 1/2] dt-bindings: HID: i2c-hid: elan: Introduce bindings for Elan eKTH6915

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Message-ID: <Yoqr59t0v23xmKby@google.com>
Date:   Sun, 22 May 2022 14:32:23 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        swboyd@...omium.org, linux-input@...r.kernel.org, mka@...omium.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: HID: i2c-hid: elan: Introduce bindings
 for Elan eKTH6915

On Thu, May 19, 2022 at 04:00:02PM -0700, Douglas Anderson 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@...omium.org>

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

Thanks.

-- 
Dmitry