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

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Message-ID: <1bc2c476-9d7b-4c87-924b-ecaed0f721de@kernel.org>
Date: Tue, 8 Oct 2024 13:23:49 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Joy Chakraborty <joychakr@...gle.com>
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 08/10/2024 12:23, Joy Chakraborty wrote:
> 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.

Platforms must have specific compatible, so this should be implied by
compatible.

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


Best regards,
Krzysztof