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Message-ID: <3925cb4b6453644c889675c20329b3477a06fcd5.camel@gmail.com>
Subject: Re: [PATCH 04/12] iio: adc: ad9467: fix reset gpio handling
From:   Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To:     David Lechner <dlechner@baylibre.com>
Cc:     nuno.sa@analog.com, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, linux-iio@vger.kernel.org,
        Olivier MOYSAN <olivier.moysan@foss.st.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Michael Hennerich <Michael.Hennerich@analog.com>
Date:   Sat, 02 Dec 2023 09:36:47 +0100
In-Reply-To: <CAMknhBGjm2ja9HOenOWi9O5Ao8qUg=gT=_Vz8CyxQ=pfNX2EJQ@mail.gmail.com>
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         <d534c3323c32d4ed2aedae19a9f101be90ef0cc7.camel@gmail.com>
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On Fri, 2023-12-01 at 11:01 -0600, David Lechner wrote:
> On Fri, Dec 1, 2023 at 2:47=E2=80=AFAM Nuno S=C3=A1 <noname.nuno@gmail.co=
m> wrote:
> >=20
> > On Thu, 2023-11-30 at 15:41 -0600, David Lechner wrote:
> > > On Tue, Nov 21, 2023 at 4:17=E2=80=AFAM Nuno Sa via B4 Relay
> > > <devnull+nuno.sa.analog.com@kernel.org> wrote:
> > > >=20
> > > > From: Nuno Sa <nuno.sa@analog.com>
> > > >=20
> > > > The reset gpio was being requested with GPIOD_OUT_LOW which means, =
not
> > > > asserted. Then it was being asserted but never de-asserted which me=
ans
> > > > the devices was left in reset. Fix it by de-asserting the gpio.
> > >=20
> > > It could be helpful to update the devicetree bindings to state the
> > > expected active-high or active-low setting for this gpio so it is
> > > clear which state means asserted.
> > >=20
> >=20
> > You could state that the chip is active low but I don't see that change=
 that
> > important for now. Not sure if this is clear and maybe that's why your =
comment.
> > GPIOD_OUT_HIGH has nothing to do with active high or low. It just means=
, "get me
> > the
> > pin in the asserted state".
> >=20
>=20
> I would assume that this bug happened in the first place because
> someone forgot GPIOD_OUT_LOW in the devicetree when they were
> developing the driver. So this is why I suggested that updating the
> devicetree binding docs so that future users are less likely to make
> the same mistake. Currently, the bindings don't even have reset-gpios
> in the examples.

Hmm, I think you're missing the point... The bug has nothing to do with dev=
icetree.
This is what was happening:

1) We were calling devm_gpiod_get_optional() with GPIOD_OUT_LOW. What this =
means is
that you get an output gpio deasserted. Hence the device is out of reset. A=
nd here is
the important part... what you have in dts does not matter. If you have act=
ive low,
it means the pin level will be 1. If you have high, the pin level is 0. And=
 this is
all handled by gpiolib for you.

2) Then, we called gpiod_direction_output(..., 1), which means set the dire=
ction out
(which is actually not needed since it was already done when getting the pi=
n) and
assert the pin. Hence, reset the device. And we were never de-asserting the=
 pin so
the device would be left in reset.

- Nuno S=C3=A1