[PATCH v11 3/7] usb: onboard-hub: add support for Microchip USB5744

[Marek Vasut]

On 11/20/24 5:22 AM, Abbarapu, Venkatesh wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Marek Vasut <marex at denx.de>
>> Sent: Tuesday, November 19, 2024 7:49 PM
>> To: Abbarapu, Venkatesh <venkatesh.abbarapu at amd.com>; u-boot at lists.denx.de
>> Cc: Simek, Michal <michal.simek at amd.com>; fabrice.gasnier at foss.st.com; git
>> (AMD-Xilinx) <git at amd.com>
>> Subject: Re: [PATCH v11 3/7] usb: onboard-hub: add support for Microchip
>> USB5744
>>
>> On 11/19/24 4:22 AM, Abbarapu, Venkatesh wrote:
>>
>> [...]
>>
>>>>>>>> Is there a matching delay requirement specified in the USB hub
>>>>>>>> datasheet or is this a workaround for some board-specific behavior ?
>>>>>>> The matching delay is not specified in the USB5744 hub document,
>>>>>>> but based on
>>>>>> testing on 2 boards with the above-mentioned delay i2c failures
>>>>>> were not
>>>> observed.
>>>>>> Is this 10ms a board-specific reset delay ?
>>>>>> Why is it in a generic driver ?
>>>>> On our boards we observed i2c failures when we set the reset delay
>>>>> as 5us and power on delay as 1ms as per the USB5744 datasheet. The
>>>>> reason of adding 10ms delay is because of i2c failures and the linux
>>>>> reference is
>>>>> https://github.com/torvalds/linux/commit/908f61bedb2c40c6d856bbfd7f8
>>>>> 70
>>>>> b967a4cb498 Do you have anything with respect to these delays, as
>>>>> you might have tested on some other boards? If anything, please let me know.
>>>> If the 10ms delay is a board specific delay, then this has to be
>>>> handled in a board specific way, not hard-coded in the driver.
>>>> Probably add some new property which specifies the extra board
>>>> specific reset delay, but be sure to run that property by the Linux kernel
>> maintainers too.
>>> Thanks. I will check how to add the board specific delay as new property.
>>
>> Add some reset-...-us , similar to what ethernet PHYs already do in DT.
> Sure...will check and initiate discussion with the Linux team.
> 
>>
>>> As this delay might be specific to the boards which we tested.
>>> There won't be any issue if we can add the default "reset_delay"(5us) and
>> "power_on_delay" (1ms) from the USB5744 datasheet, as other boards will be
>> working without any board specific delay?
>> Right, the driver has to be generic , that means it should contain delays specified in
>> the datasheet. Board specific delays have to be configured in board specific DTs.
> Thanks. I have updated the delays based on usb5744 specification in the
> [PATCH v13 3/7] usb: onboard-hub: add support for Microchip USB5744
> Please review.
V13 also enables the hub driver for Xilinx hardware, does it not ?
If so, won't doing so lead to incorrect behavior due to -- now -- too 
short delay ? I suspect you will need V14 which adds those board 
specific delays via DT for the Xilinx hardware.