Re: [PATCH v7 1/2] dt-bindings: iio: proximity: add ST VL53L1X ToF sensor

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Wed, 25 Mar 2026 14:44:13 +0100
Krzysztof Kozlowski <krzk@kernel.org> wrote:

> On 25/03/2026 14:38, Jonathan Cameron wrote:
> > On Wed, 25 Mar 2026 15:18:05 +0600
> > Sirat <email@sirat.me> wrote:
> >   
> >> On Wed, Mar 25, 2026 at 2:58 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:  
> >>>
> >>> On 25/03/2026 09:48, Sirat wrote:    
> >>>> On Wed, Mar 25, 2026 at 2:05 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:    
> >>>>>
> >>>>> On Wed, Mar 25, 2026 at 12:32:22PM +0600, Siratul Islam wrote:    
> >>>>>> Add device tree binding documentation for the STMicroelectronics
> >>>>>> VL53L1X Time-of-Flight ranging sensor connected via I2C.
> >>>>>>
> >>>>>> Make vdd-supply required. The device requires power to operate
> >>>>>> and the property should have been required from the start.    
> >>>>>
> >>>>> That's ABI break and device for many years was working fine, so this
> >>>>> should not be changed.
> >>>>>    
> >>>> Jonathan and David asked that vdd-supply be made required. I feel like
> >>>> there is a conflict here that I am not able to resolve myself.
> >>>>
> >>>> What I think about it is the binding does not correctly describe the
> >>>> hardware and we should consider this a bug and fix it.
> >>>> The driver worked because of a fallback mechanism (dummy/fake
> >>>> regulator) and not because power was optional.
> >>>>    
> >>>
> >>>
> >>> I looked at v6 and v5 and I do not see such comment for binding that
> >>> existing device should change ABI. Can you point me to it?
> >>>    
> >> "Make it required and add a note to the commit message to say why the
> >> requirement should always have been there. Devices tend not to work
> >> with no power." - Jonathan (v3:
> >> https://lore.kernel.org/linux-iio/20260322115704.10b2e0d4@jic23-huawei)
> >>
> >> "No, bindings should not depend on driver implementation." - David
> >> (When I asked if I should  drop the hard requirement in the binding,
> >> v6: https://lore.kernel.org/linux-iio/55e92148-b5de-4fb8-af0b-9476235341bc@baylibre.com/)
> >>
> >> "From the point of view of the devicetree, it doesn't matter what the
> >> driver does. It matters that the chip can't work without power. ;-)" -
> >> David (v1: https://lore.kernel.org/linux-iio/d0ec6a2f-6d30-4774-8950-15dd3c4b020b@baylibre.com)
> >>
> >> I'm not sure if this is the correct way to quote. But I have added the links.  
> > 
> > This came up a few years back - though I doubt I can track down the
> > exact discussion however.
> > 
> > From a Linux point of view we are breaking binding checks only if the
> > supply (that should always have been there as chips tend not to work
> > well without power) is not present.  We absolutely have to
> > keep the driver running whether or not the supply is specified.
> > Do other DT users provide such a constraint? I've no idea.
> > 
> > If the DT maintainer preference is leave it not required (perhaps
> > with a comment saying new users of the binding should supply it)
> > then that's fine by me. I'll keep it in mind for future similar changes.  
> 
> If this was other ABI, e.g. clock, then answer would be - do not require
> it, because that's ABI break. Therefore I would stick to that also to
> regulators. Once Rob also expressed such thoughts, although noting that
> it is not that big deal.
> 
> New device in this binding of course should require the supply.
Seems my memory was less than perfect on this : 
https://lore.kernel.org/linux-iio/20241119140409.GA1093349-robh@kernel.org/#t

Rob expressed that we are inconsistent on this, but he'd rather not
have regulators as a special case.

So let's only make this required for the new device. 

Thanks,

J

> 
> Best regards,
> Krzysztof
>