linux-kernel - Re: [PATCH v2 2/2] HID: i2c-hid: elan: Add support for Elan eKTH6915 i2c-hid touchscreens

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Message-ID: <Yov+8u5Ohrzynlx9@google.com>
Date:   Mon, 23 May 2022 14:38:58 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        swboyd@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] HID: i2c-hid: elan: Add support for Elan eKTH6915
 i2c-hid touchscreens

On Mon, May 23, 2022 at 02:23:24PM -0700, Douglas Anderson wrote:
> Like many i2c-hid touchscreen controllers, the Elan eKTH6915 has a
> reset GPIO hooked up to it. According to the datasheet, the way we're
> supposed to turn the touchscreen on is:
> 
> 1. Turn on the 3.3V supply.
> 2. Turn on the IO supply. It's OK if this is hardwired to the 3.3V
>    supply, but if it's not then it must be turned on _after_ the 3.3V
>    supply.
> 3. Wait >= 1 ms.
> 4. Deassert the reset GPIO (reset GPIO is active low, so there would
>    be a leakage path if this was deasserted _before_ the IO supply).
> 5. Wait 300 ms.
> 
> Much of the above can be handled by the generic i2c-hid-of driver, but
> the "reset" GPIO is not supported by that driver. Thus we'll do the
> same as we did for Goodix and add a new tiny driver that uses the
> i2c-hid core.
> 
> NOTE: support for this new touchscreen could theorically fit into the
> Goodix driver. I've made it a separate driver because the Elan driver
> supports _two_ regulators and it's unclear exactly how that would fit
> in with commit 18eeef46d359 ("HID: i2c-hid: goodix: Tie the reset line
> to true state of the regulator").
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>