From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Jonathan Albrieux <jonathan.albrieux@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Hartmut Knaack <knaack.h@gmx.de>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Lars-Peter Clausen <lars@metafoo.de>,
Linus Walleij <linus.walleij@linaro.org>,
"open list:IIO SUBSYSTEM AND DRIVERS" <linux-iio@vger.kernel.org>,
Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
Steve Winslow <swinslow@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Jonathan Cameron <jic23@kernel.org>
Subject: Re: [PATCH 3/3] iio: magnetometer: ak8975: Add gpio reset support
Date: Mon, 18 May 2020 20:51:29 +0300 [thread overview]
Message-ID: <CAHp75VcJ+LU_T4jRVNDBed50xaALDLNC_8brxszv5FpUGHF7+A@mail.gmail.com> (raw)
In-Reply-To: <20200518174335.GA6392@jonathan-N53SV>
On Mon, May 18, 2020 at 8:43 PM Jonathan Albrieux
<jonathan.albrieux@gmail.com> wrote:
>
> On Mon, May 18, 2020 at 07:43:17PM +0300, Andy Shevchenko wrote:
> > On Mon, May 18, 2020 at 06:01:20PM +0200, Jonathan Albrieux wrote:
> > > On Mon, May 18, 2020 at 05:55:51PM +0300, Andy Shevchenko wrote:
> > > > On Mon, May 18, 2020 at 4:38 PM Jonathan Albrieux
> > > > <jonathan.albrieux@gmail.com> wrote:
> > > >
> > > > > + gpiod_set_value_cansleep(data->reset_gpiod, 1);
> > > >
> > > > (1)
> > > >
> > > > ...
> > > >
> > > > > + /*
> > > > > + * If reset pin is provided then will be set to high on power on
> > > > > + * and to low on power off according to AK09911 datasheet
> > > > > + */
> > > >
> > > > Wording is confusing, perhaps you have to use 'asserted / deasserted'.
> > >
> > > Thank you for the suggestion, I'll be working on rewording as soon as
> > > possible.
> > >
> > > > Btw, in (1) it's also "high" (asserted). I barely understand how it's
> > > > supposed to work in all cases?
> > > >
> > > > > + reset_gpiod = devm_gpiod_get_optional(&client->dev,
> > > > > + "reset", GPIOD_OUT_HIGH);
> > > > > + if (IS_ERR(reset_gpiod))
> > > > > + return PTR_ERR(reset_gpiod);
> > > >
> > >
> > > I'm sorry but I'm not sure about what you mean by saying all cases.
> > > Currently I'm testing this driver on a msm8916 device having AK09911
> > > magnetometer. At the current stage the driver is failing on probe
> > > because reset pin is not connected to VID (as datasheet requires in case
> > > of pin not being used). In case of reset pin not asserted, register's
> > > reset is triggered resulting in empty registers, leading to probe fail.
> > > For this reason pin is asserted during power on in order to have
> > > informations in registers and deasserted before power off triggering
> > > a reset.
> > >
> > > A workaround that gets AK09911 working on device is by setting the
> > > reset pin always high on device tree. This way registers gets reset by
> > > a Power On Reset circuit autonomously and reset pin never triggers the
> > > reset.
> >
> > You need to distinguish electrical level from logical (GPIO flag defines
> > logical). So, I'm talking about active-high vs. active-low case.
> >
> > Now I re-read above, and see that here you assert the reset signal. But where
> > is desertion?
>
> Oh I see, I'll try explaining by points the proposed approach:
> - reset pin is active low
> - during power on gpio is set to 0 so the reset pin is high, thus no reset
deasserted
> - during power off gpio is set to 1 so the reset pin becomes low, thus resetting
asserted
> this is a possible solution but maybe there are other ways to achieve that,
> do you have suggestions on how to get a better approach for solving this issue?
I see now, that at requesting reset you wanted to chip be in reset
state (asserted) till driver calls power_on().
Seems everything you done is correct. Just correct terminology, please.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-05-18 18:21 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-18 13:36 [PATCH 0/3] iio: magnetometer: ak8975: Add gpio reset support Jonathan Albrieux
2020-05-18 13:36 ` [PATCH 1/3] dt-bindings: iio: magnetometer: ak8975: convert txt format to yaml Jonathan Albrieux
2020-05-18 13:36 ` [PATCH 2/3] dt-bindings: iio: magnetometer: ak8975: add gpio reset support Jonathan Albrieux
2020-05-25 8:43 ` Linus Walleij
2020-05-25 10:53 ` Jonathan Albrieux
2020-05-18 13:36 ` [PATCH 3/3] iio: magnetometer: ak8975: Add " Jonathan Albrieux
2020-05-18 14:55 ` Andy Shevchenko
2020-05-18 16:01 ` Jonathan Albrieux
2020-05-18 16:43 ` Andy Shevchenko
2020-05-18 17:43 ` Jonathan Albrieux
2020-05-18 17:51 ` Andy Shevchenko [this message]
2020-05-18 18:46 ` Jonathan Albrieux
2020-05-29 13:33 ` Pavel Machek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAHp75VcJ+LU_T4jRVNDBed50xaALDLNC_8brxszv5FpUGHF7+A@mail.gmail.com \
--to=andy.shevchenko@gmail.com \
--cc=Jonathan.Cameron@huawei.com \
--cc=devicetree@vger.kernel.org \
--cc=gregkh@linuxfoundation.org \
--cc=jic23@kernel.org \
--cc=jonathan.albrieux@gmail.com \
--cc=knaack.h@gmx.de \
--cc=lars@metafoo.de \
--cc=linus.walleij@linaro.org \
--cc=linux-iio@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pmeerw@pmeerw.net \
--cc=swinslow@gmail.com \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).