linux-kernel - Re: [Letux-kernel] [PATCH] arm: dts: gta04: add gps support

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Date:   Wed, 30 Jan 2019 21:11:38 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Johan Hovold <johan@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Benoit Cousson <bcousson@...libre.com>,
        linux-omap <linux-omap@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [Letux-kernel] [PATCH] arm: dts: gta04: add gps support

On Wed, 30 Jan 2019 15:06:12 +0100
"H. Nikolaus Schaller" <hns@...delico.com> wrote:

> Hi Andreas,
> 
> > Am 30.01.2019 um 10:02 schrieb Johan Hovold <johan@...nel.org>:
> > 
> > On Mon, Jan 28, 2019 at 05:44:29PM +0100, Andreas Kemnade wrote:  
> >> On Mon, 28 Jan 2019 08:53:56 +0100
> >> Johan Hovold <johan@...nel.org> wrote:
> >>   
> >>> On Fri, Jan 25, 2019 at 08:43:10PM +0100, Andreas Kemnade wrote:  
> >>>> The GTA04 has a w2sg0004 or w2sg0084 gps chip. Not detectable
> >>>> which one is mounted so use the compatibility entry for w2sg0004
> >>>> for all which will work for both.
> >>>> 
> >>>> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> >>>> ---
> >>>> w2sg0004 bindings (together with the corresponding support is in
> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/johan/gnss gnss-next)
> >>>> arch/arm/boot/dts/omap3-gta04.dtsi | 13 +++++++++++++
> >>>> 1 file changed, 13 insertions(+)  
> >   
> >>>> +	gps: gps {    
> >>> 
> >>> The node should be named "gnss" as per the binding.
> >>>   
> >>>> +		compatible = "wi2wi,w2sg0004";
> >>>> +		pinctrl-names = "default";
> >>>> +		pinctrl-0 = <&gps_pins>;
> >>>> +		sirf,onoff-gpios = <&gpio5 17 GPIO_ACTIVE_HIGH>;
> >>>> +		lna-supply = <&vsim>;    
> >>> 
> >>> Also, the vcc-supply is a required property.
> >>>   
> >> well, it is not require in the driver and it has different behavior
> >> (on even when not opened if on-off is there) than the lna-supply used
> >> here. So maybe fix the binding documentation?  
> > 
> > The device-tree describes hardware, and how a particular driver happens
> > to implement a binding is not relevant.
> > 
> > That said, there is a bit of an on-going, shall we say philosophical,
> > debate about this. The regulator maintainer takes a firm position that
> > all mandatory physical supplies should be represented in firmware
> > 	
> > 	https://lore.kernel.org/lkml/20181123133126.GF2089@sirena.org.uk/T/#u
> > 	https://lore.kernel.org/lkml/20180409102244.GB11532@sirena.org.uk/T/#u
> > 
> > while Rob appears to take a slightly different stance on fixed
> > regulators while admitting that this an issue which has not yet been
> > fully resolved:
> > 
> > 	https://lore.kernel.org/lkml/20180425171123.xhyoay3nu463btoq@rob-hp-laptop/T/#u
> > 
> > Since this is a new binding, and the hardware requires the vcc supply
> > and this is reflected in the binding, I think you should add a fixed
> > regulator. At least until you hear otherwise. ;)  
> 
> Assuming that there is no REGEN signal from the twl4030 unless 1V8 is also
> stable, I'd suggest as a simple solution:
> 
> 	 vcc-supply = <&vio>;
> 
> Alternatively, we could define a dedicated fixed-regulator in omap3-gta04.dtsi
> for the 3V3 rail. Which is always-on. This would allow to describe that e.g. the
> itg3200, panel and other chips and sensors are also supplied by this. But since
> no driver can really make use of it (turn on/off on demand) this is IMHO quite
> needless.
> 
well, probably better to add that regulator, so we match the real
hardware and not doing some fake here just to satisfy that binding
requirement. I will send a new version with that regulator added.

Regards,
Andreas

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