linux-kernel - Re: [PATCH v2 2/4] dt-bindings: gnss: add mediatek binding

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Date:   Wed, 13 Feb 2019 16:24:00 +0100
From:   Loys Ollivier <lollivier@...libre.com>
To:     Loys Ollivier <lollivier@...libre.com>
Cc:     Johan Hovold <johan@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, Kevin Hilman <khilman@...libre.com>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: gnss: add mediatek binding

On Mon 11 Feb 2019 at 14:17, Loys Ollivier <lollivier@...libre.com> wrote:

> On Mon 11 Feb 2019 at 08:33, Johan Hovold <johan@...nel.org> wrote:
>
>> On Mon, Jan 28, 2019 at 04:46:53PM +0100, Loys Ollivier wrote:
>>>
>>> On Fri 25 Jan 2019 at 09:07, Johan Hovold wrote:
>>>
>>> > On Thu, Jan 17, 2019 at 05:54:32PM +0100, Loys Ollivier wrote:
>>> >> Add binding for Mediatek-based GNSS receivers.
>>> >>
>>> >> Signed-off-by: Loys Ollivier <lollivier@...libre.com>
>>> >> ---
>>> >>
>>> >> v2:
>>> >> Renamed bindings from Globaltop/gtop to Mediatek/mtk.
>>> >> Moved current-speed as an optional propertie.
>>> >> Removed the status line in the example.
>>> >> Added "mediatek,mt3339" compatible.
>>
>>> >> +++ b/Documentation/devicetree/bindings/gnss/mediatek.txt
>>> >> @@ -0,0 +1,39 @@
>>> >> +Mediatek-based GNSS Receiver DT binding
>>> >> +
>>> >> +Mediatek chipsets are used in GNSS-receiver modules produced by several
>>> >> +vendors and can use UART, SPI or I2C interfaces.
>>> >> +
>>> >> +Please see Documentation/devicetree/bindings/gnss/gnss.txt for generic
>>> >> +properties.
>>> >> +
>>> >> +Required properties:
>>> >> +
>>> >> +- compatible    : Must be one of
>>> >> +
>>> >> +                        "globaltop,pa6h"
>>> >> +                        "mediatek,mt3339"
>>> >
>>> > I'm not sure it makes sense to add the GPS chip itself as it cannot be
>>> > used stand-alone AFAIU, and either not way would require a lot more
>>> > resources to be defined than what you add to this binding.
>>>
>>> OK, I find it a bit confusing to have Mediatek bindings but no
>>> compatible Mediatek SoCs.
>>> But it is true that it can't be used stand-alone. I will remove this
>>> reference and also remove it from the mtk.c driver code from this patch
>>> serie.
>>
>>> >> +Required properties (I2C):
>>> >> +- reg           : I2C slave address
>>> >> +
>>> >> +Required properties (SPI):
>>> >> +- reg           : SPI chip select address
>>> >
>>> > While the mt3339 appears to support these interfaces, the globaltop one
>>> > does not.
>>> >
>>> > Have you looked around for a small sample of mt3339-based receivers, to
>>> > see whether anyone actually provides these?
>>>
>>> Again I'm confused by the fact that it is the Mediatek bindings.
>>> Hence why I have added it and why it was not present in the v1 that was
>>> only for Globaltop.
>>
>> This is no different from the sirfstar driver for receivers based on
>> those chipsets but manufactured by various other vendors.
>>
> Indeed.
>
>>> I find it odd mentionning the chipset but not all its interfaces.
>>> I will remove these sections and only list supported interfaces (i.e.
>>> UART). Other interfaces can be added afterward if one finds a board that
>>> provides them.
>>
>> Right, but please do look around for other receivers using this chipset
>> so that we can make the binding generic enough to cover those as well
>> (e.g. by choosing representative resource names).
>>
> OK will have a look.

The only mt3339-based receivers I have found are:
- [0] Globaltop
- [1] Locosys / Pololu
They both only provide the UART interface and do not list the I2C/SPI
interfaces.

[0] https://cdn-shop.adafruit.com/datasheets/GlobalTop-FGPMMOPA6H-Datasheet-V0A.pdf
[1] https://www.pololu.com/file/0J641/LS20030~3_datasheet_v1.3.pdf

>
>> Johan



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