linux-kernel - Re: [PATCH v2 2/2] devicetree: i2c-hid: Add reset property

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Date:   Mon, 06 Nov 2017 08:10:51 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Rob Herring <robh@...nel.org>
CC:     Lin Huang <hl@...k-chips.com>, jikos@...nel.org,
        jani.nikula@...el.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, briannorris@...omium.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 2/2] devicetree: i2c-hid: Add reset property

On November 6, 2017 1:06:30 AM PST, Benjamin Tissoires <benjamin.tissoires@...hat.com> wrote:
>Hi Rob,
>
>On Nov 01 2017 or thereabouts, Rob Herring wrote:
>> On Tue, Oct 31, 2017 at 11:03:16AM +0800, Lin Huang wrote:
>> > Document a "reset" and "assert-reset-us", it can be used for
>> > driver control reset property. And reuse post-power-on-delay-ms
>> > for deassert reset delay.
>> 
>> "dt-bindings: input: " for the subject please.
>> 
>> > 
>> > Signed-off-by: Lin Huang <hl@...k-chips.com>
>> > ---
>> >  Documentation/devicetree/bindings/input/hid-over-i2c.txt | 4 +++-
>> >  1 file changed, 3 insertions(+), 1 deletion(-)
>> > 
>> > diff --git
>a/Documentation/devicetree/bindings/input/hid-over-i2c.txt
>b/Documentation/devicetree/bindings/input/hid-over-i2c.txt
>> > index 28e8bd8..6ab0eed 100644
>> > --- a/Documentation/devicetree/bindings/input/hid-over-i2c.txt
>> > +++ b/Documentation/devicetree/bindings/input/hid-over-i2c.txt
>> > @@ -31,7 +31,9 @@ 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
>> > -  before it is ready for communication. Must be used with
>'vdd-supply'.
>> > +  or deassert reset pin before it is ready for communication.
>> > +- reset: phandle of the gpio that provides for hid reset pin.
>> 
>> The kernel api takes "reset", but the property is "reset-gpios".
>
>In the same way the generic regulator interface handles vdd-supply, is
>there any generic OF handling of reset lines? As far as I can tell,
>there are 97 references of reset-gpios in my tree, and I wonder if all
>the matching drivers need to rewrite the same code to set the reset
>line
>on power on/off.
>
>I am worried because here, 1/2 writes "arbitrary" 0 and 1 to the gpios,
>and nothing prevent a manufacturer to invert the required voltages on
>the reset lines, meaning there will be a need for a new OF property.

1and 0 are logical high and low here. Gpiod API takes care of converting to the proper polarity.


Thanks.

-- 
Dmitry