Re: Fwd: USB DBC hang during earlyprintk initialization

[Mathias Nyman <mathias.nyman@linux.intel.com>]

Hi

On 12/5/25 20:49, Milan Oravec wrote:
> Hello Mathias, I've replaced cat with minicom in the script above and
> let minicom capture the file. First minicom displayed no messages,
> then I realised I need to press and hold enter to be able see messages
> sent from debug target.

You shouldn't need to do that, something is set up oddly.

> 
> Computer hangs and needs a long press of the power button to recover.
> Boot cmd used:
> linux /vmlinuz root=UUID=584262b6-b020-4e4f-95a3-1db754e28b6c
> earlyprintk=keep,xdbc2 debug ignore_loglevel sysrq_always_enabled
> force_early_printk sched_verbose usbcore.autosuspend=-1
> no_console_suspend resume=UUID=54ed98b5-56c0-4ab9-95ea-da1a9322ce49
> 
> I've attached a captured log from deminicom.
> 
> What should I try next?

early_xdbc_write() is called every time a new entry is written to console.
It only uses one transfer buffer, (one TRB).
early_xdbc_write() will block for up to 2 seconds in a udelay loop waiting
for the previous transfer to complete.

blocking for 2 seconds on every console message doesn't sound reasonable.
Maybe for the first message to make sure other side is set up and reading the data.

I'm also not sure the "keep" flag works.
Once the actual xhci driver binds to the device it will reset the controller , losing
DBC capability and console.

You could try without the keep flag, and setting timeout to 100ms instead of 2 seconds

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index 41118bba9197..515a172ba25b 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -855,7 +855,7 @@ static int xdbc_bulk_write(const char *bytes, int size)
  	xdbc_handle_events();
  
  	/* Check completion of the previous request: */
-	if ((xdbc.flags & XDBC_FLAGS_OUT_PROCESS) && (timeout < 2000000)) {
+	if ((xdbc.flags & XDBC_FLAGS_OUT_PROCESS) && (timeout < 100000)) {
  		raw_spin_unlock_irqrestore(&xdbc.lock, flags);
  		udelay(100);
  		timeout += 100;

Thanks
Mathias