Re: [PATCH 4/7] dt-bindings: gnss: add u-blox binding

[Rob Herring <robh+dt@kernel.org>]

On Wed, May 2, 2018 at 3:16 AM, Johan Hovold <johan@kernel.org> wrote:
> On Tue, May 01, 2018 at 09:05:42AM -0500, Rob Herring wrote:
>> 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.
>
> Yes, but...
>
>> > 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.
>
> ...my point was that in case there's no backup battery, you don't want
> to enable vcc (via v_bckp) at probe (and instead have the device cold
> boot whenever it's used).

Wouldn't that result in very long acquisition times? I guess I was
thinking Vcc would be always on when running and V_bckp was just for
suspend.

> Hence, the driver would need to check if the v_bckp-supply is identical
> to vcc and not enable the former at probe in that case (i.e. similar to
> if no v_bckp had been specified and we considered it optional).

I guess if that's the intended operation, then making it optional is fine.

Rob

>
>> >> > +- 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"?
>
> That's the generic function name.
>
>> Maybe just a "pin name: X" prefix so it is clear.
>
> For u-blox devices, where property-, function- and pin name coincide, I
> could just change this to:
>
> +- timepulse-gpios      : Timepulse GPIO
>
> and then for the sirfstar binding, which will be used by devices from
> multiple vendors which have decided to name their pins differently, I
> can add a "pin name: " prefix for clarity?

Sounds good.

>> > 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.
>
> I had some concerns along those lines as well, and if you agree I'll
> change the property name to on_off-gpios (or onoff-gpios) which matches
> the vendor data sheets for this pin, and which I think would be better.

Okay, just add a vendor prefix. And note that using '_' is discouraged.

Rob