Re: [PATCH 1/2] dt-bindings: usb: dwc3: Add binding for USB Gen2 de-emphasis

[Joy Chakraborty]

On Tue, Oct 8, 2024 at 5:40 PM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
>
> On 08/10/2024 13:59, Joy Chakraborty wrote:
> >>>
> >>>>
> >>>>> +    description: When set core will set Tx de-emphasis for USB Gen2
> >>>>
> >>>> And why it cannot be implied by compatible?
> >>>
> >>> As per my understanding these are tuning coefficients for de-emphasis
> >>> particular to a platform and not the dwc3 controller, hence should not
> >>> be a controller compatible.
> >>
> >> Platforms must have specific compatible, so this should be implied by
> >> compatible.
> >
> > Maybe I am using the word "platform" incorrectly here, what I
> > understand is that the same controller(in a chip) when used on 2
> > different physical form factors might need different deemphasis
>
> You mean boards? This is board-level property?

Yes, the USB controller can be paired with different phys in a SoC and
used on different board layouts where we should be able to drive
different de-emphasis coefficients to the phy as per the link
equalization requirements is my understanding.

>
> > coefficient values to be passed to its Phy. Someone could correct me
> > from the USB link stand point if I am mistaken here.
> >
>
> Then please point me to the upstream DTS boards using these properties.
> Lore link is enough, if board or DTS change is being upstreamed.
>

The DTS change is not being upstreamed currently.
But this change would help bring up a new or development board where
USB compliance is being run and this parameter needs tuning,  hence
being able to upstream this would help.

> Best regards,
> Krzysztof
>