linux-kernel - [PATCH 1/2] dt-bindings: HID: i2c-hid: Add the ability to control a reset GPIO

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Message-Id: <20201014164203.1.I1c2d6236990449717b861539a2234354153b1656@changeid>
Date:   Wed, 14 Oct 2020 16:42:20 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     jkosina@...e.cz, benjamin.tissoires@...hat.com,
        gregkh@...uxfoundation.org
Cc:     kai.heng.feng@...onical.com, linux-input@...r.kernel.org,
        hdegoede@...hat.com, andrea@...gia.bo.it, swboyd@...omium.org,
        Douglas Anderson <dianders@...omium.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] dt-bindings: HID: i2c-hid: Add the ability to control a reset GPIO

Apparently some devices connected via i2c-hid have timing requirements
around when a reset GPIO should be asserted to them.  The diagram I
have seen, which I believe is from a Goodix device, looked like this:

         +----------------------------------
         |
AVDD ----+
               +------------------------------
         | (a) |
RESET ---------+
                     +-------------
               | (b) |
I2C comm OK ---------+

Where (a) is 10 ms and (b) is 120 ms.

Let's add the ability to specify these timings to the devicetree
bindings.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
I notice this bindings file is still a ".txt" file.  Some searching on
The Internets(TM) shows that Rob has maybe started a conversion 5
years ago [1], but that looks ancient.  I can try to put something
together if need be, or we can just land this fix.  ;-)

Note that the .txt version of the bindings seems to indicate that
anyone using one of the optional properties is supposed to declare
their special compatible string.  I'm not sure if that's still
considered important or not?  Once you manage to get these devices
powered on and talking i2c they self-describe themselves...

[1] https://kernel.googlesource.com/pub/scm/linux/kernel/git/robh/linux/+/refs/heads/dt-yaml/Documentation/devicetree/bindings/hid/hid-over-i2c.yaml

 Documentation/devicetree/bindings/input/hid-over-i2c.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/hid-over-i2c.txt b/Documentation/devicetree/bindings/input/hid-over-i2c.txt
index c76bafaf98d2..6fca39aa8cc6 100644
--- a/Documentation/devicetree/bindings/input/hid-over-i2c.txt
+++ b/Documentation/devicetree/bindings/input/hid-over-i2c.txt
@@ -32,6 +32,11 @@ device-specific compatible properties, which should be used in addition to the
 - vdd-supply: phandle of the regulator that provides the supply voltage.
 - post-power-on-delay-ms: time required by the device after enabling its regulators
   or powering it on, before it is ready for communication.
+- reset-gpios: GPIOs to assert to reset the device. This GPIO is asserted when
+  the device is powered off and released post-power-on-delay-ms after
+  enabling the regulators.
+- post-gpio-reset-delay-ms: After deasserting reset we'll delay for this many
+  more milliseconds.
 
 Example:
 
-- 
2.28.0.1011.ga647a8990f-goog