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

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Message-ID: <2e03b43e-5917-4581-9aed-780dec9e3ea9@amd.com>
Date: Fri, 13 Jun 2025 11:13:48 +0200
From: Michal Simek <michal.simek@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
 Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 gregkh@...uxfoundation.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org
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 6/13/25 10:47, Krzysztof Kozlowski wrote:
> 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?

Here is datasheet.

https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/DataSheets/USB5744-Data-Sheet-DS00001855.pdf

10.6.3 chapter

minimum assert time is 5us this corresponds to reset-delay-us and then there is 
requirement for minimum 1ms for configuration strap.
On Kria platforms 5us and 1ms is used in U-Boot usb onboard driver but that 
times needs to be extended to be able to configure hub over i2c.

Linux current has hardcoded value 0us/10ms.

  33 static const struct onboard_dev_pdata microchip_usb5744_data = {
  34         .reset_us = 0,
  35         .power_on_delay_us = 10000,
  36         .num_supplies = 2,
  37         .supply_names = { "vdd", "vdd2" },
  38         .is_hub = true,
  39 };

Thanks,
Michal