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

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Message-ID: <CAOSNQF148N5meoFZkbGKoMXMZ62kf=JOV+1r0GCsep3DPP_Lrw@mail.gmail.com>
Date: Tue, 8 Oct 2024 15:53:07 +0530
From: Joy Chakraborty <joychakr@...gle.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Thinh Nguyen <Thinh.Nguyen@...opsys.com>, Felipe Balbi <balbi@...nel.org>, linux-usb@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: usb: dwc3: Add binding for USB Gen2 de-emphasis

On Mon, Oct 7, 2024 at 8:26 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 07/10/2024 15:55, Joy Chakraborty wrote:
> > PIPE4 spec defines an 18bit de-emphasis setting to be passed from
> > controller to the PHY.
> > TxDeemph[17:0] is split as [5:0] C-1, [11:6] C0, [17:12] C+1 for 3 tap
> > filter used for USB Gen2(10GT/s).
> >
> > Signed-off-by: Joy Chakraborty <joychakr@...gle.com>
> > ---
> >  Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > index 1cd0ca90127d..a1f1bbcf1467 100644
> > --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > @@ -190,6 +190,18 @@ properties:
> >        - 1 # -3.5dB de-emphasis
> >        - 2 # No de-emphasis
> >
> > +  snps,tx_gen2_de_emphasis_quirk:
>
> No underscores.

Ack, will fix it with a follow up patch.

>
> > +    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.
Similar to the property defined right above this definition which is
from PIPE3 spec for USB Gen1.

Thanks
Joy
>
> > +    type: boolean
> > +
> Best regards,
> Krzysztof
>