Re: Explicit status phase for DWC3

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Tue, Jan 24, 2023, Dan Scally wrote:
> Hi Thinh
> 
> 
> I'm trying to update the DWC3 driver to allow the status phase of a
> transaction to be explicit; meaning the gadget driver has the choice to
> either Ack or Stall _after_ the data phase so that the contents of the data
> phase can be validated. I thought that I should be able to achieve this by
> preventing dwc3_ep0_xfernotready() from calling dwc3_ep0_do_control_status()
> (relying on an "explicit_status" flag added to the usb_request to decide
> whether or not to do so) and then calling it manually later once the data
> phase was validated by the gadget driver (or indeed userspace). A very
> barebones version of my attempt to do that looks like this:
> 

We shouldn't do this. At the protocol level, there must be better ways
to do handshake than relying on protocol STALL _after_ the data stage.
Note that not all controllers support this.

Thanks,
Thinh