linux-kernel - Re: [PATCH] dt-bindings: usb: microchip,usb5744: Add support for configurable board reset delays

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Message-ID: <f1b83b96-7cac-4014-b791-e073d2299c01@kernel.org>
Date: Fri, 13 Jun 2025 10:47:03 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 gregkh@...uxfoundation.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, michal.simek@....com
Cc: linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, git@....com
Subject: Re: [PATCH] dt-bindings: usb: microchip,usb5744: Add support for
 configurable board reset delays

On 05/06/2025 20:29, Radhey Shyam Pandey wrote:
> Introduce 'reset-delay-us' and 'power-on-delay-us' properties. Default
> delays in datasheet are not good enough for Xilinx Kria KR260 Robotics
> Starter Kit (and others) so there is a need to program board specific
> reset and power on delay via DT.
> 
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@....com>
> ---
> Taken reference from mdio.yaml[1]
> [1]: Documentation/devicetree/bindings/net/mdio.yaml
> ---
>  .../devicetree/bindings/usb/microchip,usb5744.yaml   | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml b/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
> index c68c04da3399..94a2bebd32da 100644
> --- a/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
> +++ b/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
> @@ -52,6 +52,16 @@ properties:
>      description:
>        phandle of an usb hub connected via i2c bus.
>  
> +  reset-delay-us:
> +    description:
> +      RESET pulse width in microseconds.

I don't understand - there is no user for this in USB. Why do we need an
ABI if no one ever uses it (and commit msg should clearly explain that)?

> +
> +  power-on-delay-us:

No user here, either. Plus I just wonder if you are mixing here RC
delays or regulator ramp delays, because datasheet does not mention any
delay.

Can you point me to datasheet page explaining these delays?



Best regards,
Krzysztof