kgdb debug with ttyUSB0 instead of ttyS0

[greg@kroah.com (Greg KH)]

On Wed, Apr 26, 2017 at 01:23:55PM +0200, Oliver Graute wrote:
> On 26/04/17, Greg KH wrote:
> > On Tue, Apr 25, 2017 at 11:11:38PM +0200, Oliver Graute wrote:
> > > Hello list,
> > > 
> > > i'am using a null modem cable with two usb to serial converts on both
> > > ends between my develop and my target machine. The connection is fine.
> > > On both machines the serial interface is /dev/ttyUSB0 for this connection.
> > > 
> > > On the target machine I try to enable kgdboc
> > > 
> > > echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
> > > 
> > > but only got:
> > > 
> > > echo write error: No such device
> > > 
> > > if I try:
> > > 
> > > echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
> > > 
> > > is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?
> > 
> > USB needs interrupts in order to run properly, which kgdb doesn't enable
> > when you stop the target, for obvious reasons :)
> 
> ok that make sense
> 
> > Stick to a "real" serial connection and you should be fine.
> 
> thats not so easy. Even the old notebooks today lacks a "real" serial
> connection. Perhaps I should use a raspberry as target. There I can get
> a serial over the gpios.

Why do you need to use a notebook where Linux works already for kgdb?
That's traditionally only used to bring up new hardware platforms.

Also, there is USB serial debugging cables as there is a special mode in
the USB 2 and 3 controllers that can be enabled to handle serial
messages without interrupts for console/printk early messages that
people use.  The cables are not cheap to enable this, but worth it if
you have to debug this type of target system.

Good luck!

greg k-h