Re: Cypress CDC ACM serial port not working correctly with autosuspend

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On 23.03.23 22:32, Michael Laß wrote:
Am Donnerstag, dem 23.03.2023 um 14:53 +0100 schrieb Oliver Neukum:

I am asking because the device says that it is bus powered.
That is, are we putting the device into some sleep state?

This got me thinking. I am observing the behavior on a ZedBoard, a
development board that contains a Xilinx Zynq SoC and the Cypress UART
chip connected to that SoC. I now looked into the schematic of that

Are those devices out in the wild? That is can one buy them or did
you get it through development channels?

The chip is a CY7C64225-28PVXC and the datasheet has a section on USB
suspend and resume: When suspended, a separate WAKE input pin has to be
set high to issue a remote wake-up. The designers of the ZedBoard have
tied this pin to ground...

That is technically allowed, though disappointing, but then you cannot advertise
"remote wakeup" in the device descriptor.

So the chip behaves as documented. If any, this is an issue with the
board design. Nothing the kernel could work around. Sorry, I hope I
haven't stolen too much of your time.

The kernel could work around it. We could quirk the device to ignore
the remote wakeup bit from this particular device based on ID.
RESET_RESUME would do that, albeit with side effects.

If such devices are found on sale we need to do something.


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