Re: ttyACM: disabled by hub (EMI?), re-enabling... Causes garbage chars & disconnect

[Joakim Tjernlund <Joakim.Tjernlund@infinera.com>]

On Tue, 2020-05-26 at 18:46 +0200, Joakim Tjernlund wrote:
> On Tue, 2020-05-26 at 12:14 +0200, Oliver Neukum wrote:
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> > 
> > 
> > Am Dienstag, den 26.05.2020, 08:59 +0000 schrieb Joakim Tjernlund:
> > > On Tue, 2020-05-26 at 10:47 +0200, Oliver Neukum wrote:
> > > > Am Montag, den 25.05.2020, 16:49 +0000 schrieb Joakim Tjernlund:
> > > > 
> > > > > To be clear, I can pull the cable and put it back and there are no garbage chars.
> > > > > There is also this error:
> > > > > [Wed May 20 14:03:25 2020] cdc_acm 1-6.3:1.1: acm_ctrl_irq - usb_submit_urb failed: -19
> > > > > [Wed May 20 14:03:25 2020] usb 1-6-port2: attempt power cycle
> > > > > [Wed May 20 14:03:26 2020] usb 1-6.3: USB disconnect, device number 86
> > > > > [Wed May 20 14:03:26 2020] cdc_acm 1-6.3:1.1: failed to set dtr/rts
> > > > > 
> > > > > Should not this auto reenable emulate reattaching the USB cable?
> > > > 
> > > > Hi,
> > > > 
> > > > yes it should. You find the garage characters after the EMI event. How
> > > > sure are you that they arrive after the event and not during the event?
> > > > 
> > > 
> > > Don't known how to determine that?
> > > I can say that
> > >    acm_ctrl_irq - usb_submit_urb failed: -19
> > 
> > -19 is -ENODEV
> > 
> > The driver thinks tries to resubmit the URB asking for control
> > messages.
> > Basically you are seeing error handling starting and failing due
> > to a subsequent disconnect.
> > 
> > > and
> > >    cdc_acm 1-6.3:1.1: failed to set dtr/rts
> > > are unique to this EMI event though. It does not feel like this
> > > reenabling follow the same procedure as a cable pull?
> > > As I can only see the above two errors I think we should get rid of
> > > these first.
> > 
> > The timing is different and if there is EMI transfer can end
> > in errors and cause error handling to kick in. You are seeing
> > symptoms. You can try enabling dynamic debugging to get
> > a better log.
> > 
> >         Regards
> >                 Oliver
> > 
> 
> Tried som dynamic debug for module cdc_acm got something I cannot parse:
> [Tue May 26 18:24:30 2020] cdc_acm 1-6.3:1.1: ttyACM0: USB ACM device
> [Tue May 26 18:24:30 2020] cdc_acm 1-6.3:1.1: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7, result 7
> [Tue May 26 18:24:43 2020] usb 1-6.2: new high-speed USB device number 36 using xhci_hcd
> [Tue May 26 18:24:43 2020] cdc_ether 1-6.2:1.0 usb0: register 'cdc_ether' at usb-0000:00:14.0-6.2, CDC Ethernet Device, 92:d1:c9:b4:91:d5
> [Tue May 26 18:24:43 2020] IPv6: ADDRCONF(NETDEV_UP): usb0: link is not ready
> [Tue May 26 18:25:40 2020] cdc_acm 1-6.3:1.1: acm_ctrl_msg - rq 0x22, val 0x3, len 0x0, result 0
> [Tue May 26 18:25:40 2020] cdc_acm 1-6.3:1.1: acm_tty_set_termios - set line: 115200 0 0 8
> [Tue May 26 18:25:40 2020] cdc_acm 1-6.3:1.1: acm_ctrl_msg - rq 0x20, val 0x0, len 0x7, result 7
> [Tue May 26 18:25:42 2020] cdc_acm 1-6.3:1.1: acm_ctrl_irq - urb shutting down with status: -2
> [Tue May 26 18:25:42 2020] cdc_acm 1-6.3:1.2: acm_read_bulk_callback - urb shutting down with status: -2
> ....
> 
> I do note one thing in:
> 
> First connect after power on for the gadget I see some garbage chars when connecting with cu.
> However, if I just do a "cat /dev/ttyACM0", Ctrl-C and then cu I there are no garbage chars.
> 
> It feels like the gadget is spewing some garbage at power on and this gets saved in hosts cdc_acm, once
> I open /dev/ttyACM0 for write, these gets echoed back to the gadget.
> If so, cdc_acm fails to clear its buffers before the first open, does this make sense to you?
> 

Got some evidence now, I change the default baud rate form 9600 to 115200 in cdc_acm and now
I can see(instead of garbage chars):
cu usbacm0
Connected.
^@



U-Boot SPL


This "u-boot SPL" is the first thing u-boot writes and somehow this is remembered, I assume, by cdc_acm 
and gets echoed back when I open ttyACM0

 Jocke