RE: [PATCH 1/2] dt-bindings: phy: imx8mq-usb: add phy tuning properties

[Jun Li]

> -----Original Message-----
> From: Johannes Zink <j.zink@xxxxxxxxxxxxxx>
> Sent: Tuesday, April 11, 2023 10:23 PM
> To: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>;
> vkoul@xxxxxxxxxx; kishon@xxxxxxxxxx; shawnguo@xxxxxxxxxx;
> s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> dl-linux-imx <linux-imx@xxxxxxx>; robh+dt@xxxxxxxxxx;
> krzysztof.kozlowski+dt@xxxxxxxxxx; Jun Li <jun.li@xxxxxxx>; Bough Chen
> <haibo.chen@xxxxxxx>; linux-phy@xxxxxxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/2] dt-bindings: phy: imx8mq-usb: add phy tuning
> properties
>
> Hi Krzystof,
>
> thank you for your explanations. As I'm still quite new to writing bindings,
> I still have some questions:
>
> On Fri, 2023-04-07 at 11:03 +0200, Krzysztof Kozlowski wrote:
> > On 05/04/2023 14:14, Johannes Zink wrote:
> > > Hi Krysztof,
> > >
> > > thanks for your review, please find my questions below.
> > >
> > > On Wed, 2023-04-05 at 13:51 +0200, Krzysztof Kozlowski wrote:
> > > > [snip]
> > > > >        A phandle to the regulator for USB VBUS.
> > > > >
> > > > > +  fsl,phy-tx-vref-tune:
> > > > > +    description:
> > > > > +      HS DC Voltage level adjustment
> > > >
> > > > "Level" in what units?
> > > >
> > >
> > > The datasheet just shows percent, ranging from -6 to +24%, in 2%
> > > increments. What unit would you suggest?
> >
> > percent
> >
> https://gith/
> >
> ub.com%2Fdevicetree-org%2Fdt-schema%2Fblob%2Fmain%2Fdtschema%2Fschemas
> > %2Fproperty-units.yaml&data=05%7C01%7Cjun.li%40nxp.com%7Ca2e1e5bb6a78
> 4
> >
> de5941d08db3a9847d0%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63816
> >
> 8197947407580%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2lu
> >
> MzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kY4dXkOHRs9k%
> > 2BeUQ5iixLYsNC8UotIgq6eOPGjbf01o%3D&reserved=0
>
> I am still a bit confused how to use this properly. How can I restrict the
> values to multiples of 2 in order to avoid illegal values?
>
> At the moment the only thing I could come up with is something like
>
> fsl,phy-tx-vref-tune-percent:
>   description: |
>     Adjusts the high-speed DC level voltage
>   $ref: /schemas/types.yaml#/definitions/int32
>   minimum: -6
>   maximum: 24
>   default: 0
>
> Does something like this work? I am not quite sure if I am on the right track
> here, especially as this requires a signed int, of which I have not seen
> many examples so far.
>
> Also, as far as the description is concerned: This is almost the entire
> information I there is in the datasheet. As I try to upstream some of the
> vendor downstream patches, I do not have any additional information.
>
> >
> > >
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > > +    enum: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
> > > > > 15,
> > > > > 16]
> > > > > +
> > > > > +  fsl,phy-tx-rise-tune:
> > > > > +    description:
> > > > > +      HS Transmitter Rise/Fall Time Adjustment
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > > +    enum: [0, 1, 2, 3]
> > > > > +
> > > > > +  fsl,phy-tx-preemp-amp-tune:
> > > > > +    description:
> > > > > +      HS Transmitter Pre-Emphasis Current Control
> > > >
> > > > If this is current then use standard unit suffixes.
> > >
> > > According to the datasheet this is in "unit amonts" of 600uA,
> > > basically 0x600uA, 1x600uA etc. Should I just suffix it with uA
> > > then?
> >
> > Yes
> >
> >
> https://gith/
> >
> ub.com%2Fdevicetree-org%2Fdt-schema%2Fblob%2Fmain%2Fdtschema%2Fschemas
> > %2Fproperty-units.yaml&data=05%7C01%7Cjun.li%40nxp.com%7Ca2e1e5bb6a78
> 4
> >
> de5941d08db3a9847d0%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63816
> >
> 8197947407580%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2lu
> >
> MzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kY4dXkOHRs9k%
> > 2BeUQ5iixLYsNC8UotIgq6eOPGjbf01o%3D&reserved=0
> >
> > The register values can work sometimes fine but also do not scale at
> > all. For any other variant all the meanings will differ. Any other
> > IMX8
> > phy will need new bindings and new description/values for your
> > register-like-fields.
>
> I think this particular property should work, probably its something like
>
> fsl,phy-tx-preemp-amp-tune-microamps:
>   description: |
>     Transmitter Pre-Emphasis Current Control
>     Controls the amount of current sourced to DPn and DMn after a J-to-
> K or K-to-J transition.
>   $ref: /schemas/types.yaml#/definitions/uint32
>   minimum: 0
>   maximum: 1800
>   default: 0
>
> What's the right way to communicate that the value is in multiples of 600uA
> and that this is only an approximate Value? Add some free-text to the
> description?
>
>
> For some other properties, such as fsl,phy-pcs-tx-swing-full or
> fsl,phy-pcs-tx-deemph-3p5db the datasheet provides no information at all,
> neither on the unit nor on a valid range. What is the proper way for something
> like them (I try to get some of the freescale downstream patches to mainline,
> but they did not even provide bindings for their
> driver...)

I will check with internal design team for those not well documented
properties.

Li Jun
>
>
> For fsl,phy-comp-dis-tune-percent, the actual values to not map well to
> integer amount of percent, but I have not found a permill in property- units.
> Also, as the steps appear quite arbitrary large, what is the correct way
> of restricting the values to valid values that the hardware can actually
> support? As reference, I have only seen stuff like the st,trim-hs-current
> in Documentation/devicetree/bindings/phy/phy-stm32-
> usbphyc.yaml so far...
>
> Thanks for helping me and best regards
> Johannes
>
>
> >
> > Best regards,
> > Krzysztof
> >
> >
> >
>
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