Re: [PATCH 1/2] dt-bindings: usb: usb251xb: add documentation for reset-delay-us

[Richard Leitner - SKIDATA <Richard.Leitner@skidata.com>]

On Tue, May 03, 2022 at 09:49:36AM +0200, Daniels Umanovskis wrote:
> On 5/3/22 2:20 AM, Rob Herring wrote:
> > My first question is whether this is board specific? If the default or
> > what the reference manual says is 500us, but you have a case needing
> > 600us, why not just change the driver. I don't think this really needs
> > tuning to each board unless the delay becomes noticeable.
> 
> This isn't a board specific issue. I detected the issue on a board we've
> been using for a long time, it's due to a specific batch of USB2512 hubs.
> We've had several batches of these hubs that were fine, but more recently
> received a batch produced in late 2021 and the hubs in this batch do not
> become responsive to I2C within the expected 500us.

What's the maximum timeout you've observed?

I guess it would be the simpler and "better" approach to just increase
the timeout in the driver (if it's not too much above the 500µs).

> 
> I arrived at that by using an oscilloscope to observe how soon after
> deasserting the reset signal the USB hub is able to respond to I2C. Most of
> the 2512s we have do that within 500us, the latest batch doesn't.
> 

regards;rl