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.
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.
