linux-kernel - Re: [PATCH 1/4] dt-bindings: phy: qcom,snps-eusb2-repeater: Document qcom,tune-res-fsdif

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Message-Id: <DB6J86NHFTNT.31MFYDTZ6B4O0@fairphone.com>
Date: Tue, 08 Jul 2025 10:31:35 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Krzysztof Kozlowski" <krzk@...nel.org>
Cc: "Vinod Koul" <vkoul@...nel.org>, "Kishon Vijay Abraham I"
 <kishon@...nel.org>, "Rob Herring" <robh@...nel.org>, "Krzysztof Kozlowski"
 <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>, "Abel Vesa"
 <abel.vesa@...aro.org>, <~postmarketos/upstreaming@...ts.sr.ht>,
 <phone-devel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
 <linux-phy@...ts.infradead.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] dt-bindings: phy: qcom,snps-eusb2-repeater:
 Document qcom,tune-res-fsdif

On Tue Jul 8, 2025 at 10:21 AM CEST, Krzysztof Kozlowski wrote:
> On Tue, Jul 08, 2025 at 10:13:24AM +0200, Krzysztof Kozlowski wrote:
>> On Wed, Jun 25, 2025 at 11:14:56AM +0200, Luca Weiss wrote:
>> > Document the FS Differential TX Output Resistance Tuning value found on
>> > the eUSB2 repeater on Qualcomm PMICs.
>> > 
>> > Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>> > ---
>> >  Documentation/devicetree/bindings/phy/qcom,snps-eusb2-repeater.yaml | 6 ++++++
>> >  1 file changed, 6 insertions(+)
>> > 
>> > diff --git a/Documentation/devicetree/bindings/phy/qcom,snps-eusb2-repeater.yaml b/Documentation/devicetree/bindings/phy/qcom,snps-eusb2-repeater.yaml
>> > index 27f064a71c9fb8cb60e8333fb285f0510a4af94f..6bfd11657e2992735998063b3ca390e04a03930d 100644
>> > --- a/Documentation/devicetree/bindings/phy/qcom,snps-eusb2-repeater.yaml
>> > +++ b/Documentation/devicetree/bindings/phy/qcom,snps-eusb2-repeater.yaml
>> > @@ -52,6 +52,12 @@ properties:
>> >      minimum: 0
>> >      maximum: 7
>> >  
>> > +  qcom,tune-res-fsdif:
>> > +    $ref: /schemas/types.yaml#/definitions/uint8
>> > +    description: FS Differential TX Output Resistance Tuning
>> 
>> Resistance is in Ohms, tuning could be in dB, so I wonder what are the
>> actual units here. Neither commit msg nor this description helps me to
>> understand that.
>
> I checked and the values are in Ohms.

Yes it's Ohms but not 0x00 = 0 ohms, and it's also an offset in ohms
from the nominal value according to the Hardware Register Description I
have, e.g. 0x7 = -12.1ohm from the default

I can try and create bindings using these Ohm offset values, I didn't
worry about it too much since the other tuning values in these bindings
are also just register values, presumably from before Konrad had access
to the docs.

Regards
Luca

>
> Best regards,
> Krzysztof