linux-kernel - Re: [PATCH 1/3] dt-bindings: iio: imu: mpu6050: Add level shifter

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Date:   Mon, 25 Sep 2023 20:02:36 +0200
From:   Andreas Kemnade <andreas@...nade.info>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <jic23@...nel.org>, <lars@...afoo.de>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <bcousson@...libre.com>, <tony@...mide.com>,
        <jean-baptiste.maneyrol@....com>, <chenhuiz@...s.com>,
        <andy.shevchenko@...il.com>, <linux-iio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 1/3] dt-bindings: iio: imu: mpu6050: Add level shifter

On Mon, 25 Sep 2023 14:21:57 +0100
Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:

> On Mon, 25 Sep 2023 14:24:32 +0200
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
> > On 25/09/2023 13:02, Andreas Kemnade wrote:  
> > > On Mon, 25 Sep 2023 11:28:52 +0100
> > > Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> > >     
> > >> On Mon, 25 Sep 2023 08:54:08 +0200
> > >> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> > >>    
> > >>> On 25/09/2023 00:25, Andreas Kemnade wrote:      
> > >>>> Found in ancient platform data struct:
> > >>>> level_shifter: 0: VLogic, 1: VDD
> > >>>>
> > >>>> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > >>>> ---
> > >>>>  .../devicetree/bindings/iio/imu/invensense,mpu6050.yaml         | 2 ++
> > >>>>  1 file changed, 2 insertions(+)
> > >>>>
> > >>>> diff --git a/Documentation/devicetree/bindings/iio/imu/invensense,mpu6050.yaml b/Documentation/devicetree/bindings/iio/imu/invensense,mpu6050.yaml
> > >>>> index 1db6952ddca5e..6aae2272fa15c 100644
> > >>>> --- a/Documentation/devicetree/bindings/iio/imu/invensense,mpu6050.yaml
> > >>>> +++ b/Documentation/devicetree/bindings/iio/imu/invensense,mpu6050.yaml
> > >>>> @@ -48,6 +48,8 @@ properties:
> > >>>>  
> > >>>>    mount-matrix: true
> > >>>>  
> > >>>> +  invensense,level-shifter: true        
> > >>>
> > >>> It does not look like you tested the bindings, at least after quick
> > >>> look. Please run `make dt_binding_check` (see
> > >>> Documentation/devicetree/bindings/writing-schema.rst for instructions).
> > >>> Maybe you need to update your dtschema and yamllint.
> > >>>
> > >>> Best regards,
> > >>> Krzysztof
> > >>>
> > >>>       
> > >>
> > >> Also this one isn't obvious - give it a description in the binding doc.
> > >>
> > >> I'm not sure of the arguement for calling it level shift in general.
> > >>    
> > > I have no more descrption than the old source (see the citation from there)
citation = line from ancient pdata struct comment cited in the commit message.

> > > https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-9150-Register-Map.pdf    
> > 
> > I could not find any reference to level shift in this manual. To which
> > page and part do you refer?
> >
> > > 
> > > does not list it. But that bit is needed to get things to work what also does the
> > > vendor kernel do.
> > > 
> > > What could be a better descrption?    
> > 
> > I don't know, but something reasonable to you should be put there.  
> 
> The text you have in the commit log seems better than nothing.
> I suspect it's internally wiring VDD to VDDIO. Normally people just
> connect both power supplies to same supply if they want to do that,
> but maybe there was a chip variant that didn't have enough pins?
> 
> If you have the device, can you see it actually matches the packaging
> types in the manual?
> 
packaging matches. It is just as usual. I think VLogic (=VDDIO) would be 1.8V
while VDD needs to be something higher, so I guess here it might be 3.3V.
There are some slight hints about level shifting here:
https://product.tdk.com/system/files/dam/doc/product/sensor/mortion-inertial/imu/data_sheet/mpu-9150-datasheet.pdf
page 37. The aux i2c bus seem to run at levels till VDD. But here, there
seems to be nothing at the aux i2c bus besides that internal magnetometer.

Regards,
Andreas