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From:   Rob Herring <robh+dt@kernel.org>
Date:   Tue, 1 May 2018 09:05:42 -0500
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Subject: Re: [PATCH 4/7] dt-bindings: gnss: add u-blox binding
To:     Johan Hovold <johan@kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Andreas Kemnade <andreas@kemnade.info>,
        Arnd Bergmann <arnd@arndb.de>,
        "H . Nikolaus Schaller" <hns@goldelico.com>,
        Pavel Machek <pavel@ucw.cz>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org
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On Thu, Apr 26, 2018 at 4:10 AM, Johan Hovold <johan@kernel.org> wrote:
> On Wed, Apr 25, 2018 at 01:16:58PM -0500, Rob Herring wrote:
>> On Tue, Apr 24, 2018 at 11:34 AM, Johan Hovold <johan@kernel.org> wrote:
>> > Add binding for u-blox GNSS receivers.
>> >
>> > Note that the u-blox product names encodes form factor (e.g. "neo"),
>> > chipset (e.g. "8") and variant (e.g. "q"), but that only formfactor and
>> > chipset is used for the compatible strings (for now).
>> >
>> > Signed-off-by: Johan Hovold <johan@kernel.org>
>> > ---
>> >  .../devicetree/bindings/gnss/u-blox.txt       | 31 +++++++++++++++++++
>> >  .../devicetree/bindings/vendor-prefixes.txt   |  1 +
>> >  2 files changed, 32 insertions(+)
>> >  create mode 100644 Documentation/devicetree/bindings/gnss/u-blox.txt
>> >
>> > diff --git a/Documentation/devicetree/bindings/gnss/u-blox.txt b/Documentation/devicetree/bindings/gnss/u-blox.txt
>> > new file mode 100644
>> > index 000000000000..bb54b83a177f
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/gnss/u-blox.txt
>> > @@ -0,0 +1,31 @@
>> > +u-blox GNSS Receiver DT binding
>> > +
>> > +The u-blox GNSS receivers can use UART, DDC (I2C), SPI and USB interfaces.
>> > +
>> > +Please see Documentation/devicetree/bindings/gnss/gnss.txt for generic
>> > +properties.
>> > +
>> > +Required Properties:
>> > +
>> > +- compatible   : Must be one of
>> > +
>> > +                       "u-blox,neo-8"
>> > +                       "u-blox,neo-m8"
>> > +
>> > +- vcc-supply   : Main voltage regulator (VCC)
>>
>> What about V_BCKP?
>
> That's the backup supply for for the RTC and batter-backed RAM. In
> configurations where a battery is not used it should be connected to
> VCC.
>
> How would you model that? I can enable a vbckp regulator at probe, but
> what if someone then accurately describes the corresponding pin as being
> connected to VCC?

You mean how to model a battery? It would just be a 'regulator'
because the regulator binding covers any supply really.

Then you just set both rails to the same supply phandle.

> I guess we can check if the regulators are identical,
> and then just have the driver ignore V_BKUP. Knowing whether there is
> a (hopefully charged) battery connected could be useful.

Regulators are ref counted, so just enable it twice. Or the driver can
just ignore it until it supports battery backup.

> I can't seem to find any other bindings that describe battery supplies,
> but I'll add it here.

There must be some. But then the battery and charger bindings are not
in the best shape.

>> > +
>> > +Optional Properties:
>>
>> reg is required if using I2C, SPI, or USB.
>
> I'll add that (even if there is no driver support for these yet).
>
>> Datasheet also shows an interrupt pin.
>
> Not used currently, but I'll add it to the binding as well.
>
>> > +
>> > +- timepulse-gpios      : Timepulse (e.g. 1PPS) GPIO (TIMEPULSE)
>>
>> Why the 3rd "TIMEPULSE"?
>
> That's the pin name, which in this case is identical to the property
> name, so I'll drop it here.

Then what is the 2nd "Timepulse"?

Maybe just a "pin name: X" prefix so it is clear.

> Take a look at the sirf binding; vendors use different names for their
> timepulse pins and in that case I added the actual pin names (1PPS, TM)
> in parenthesis after the description.
>
> Note that I mentioned "timepulse-gpios" in the generic binding with the
> intent of trying to enforce a generic name for pins with such a
> function (similarly for "enable-gpios", which I guess is already
> established).

Yes, I think that's good.

Though with the enable-gpios I was debating the name for sirfstar a
bit because it isn't the normal drive it active to enable, but rather
a pulse to enable or disable.

Rob