mabe a bug in kernel 5.4 since patchlevel 159 - dma error because use ttynull?

[Simon Lindhorst]

Hello all,


when I updated my Kernel from version 5.4.155 to 5.4.215 I get an 
strange xhci error:

/xhci-hcd f10f0000.usb3: ERROR unknown event type 37//
//xhci-hcd f10f0000.usb3: ERROR Transfer event TRB DMA ptr not part of 
current TD ep_index 2 comp_code 13//
/

After a lot of this messages, my hardware makes a reboot without any 
more outputs.

The error only occures when i add /console=null/ to my kernel bootargs. 
When I add instead console=/ttyS0,115200/ no error occured.

Now I go back in kernelversions. The error occured first in version 
5.4.159. Between patchlevel 158 and 159 there is a change:

/--- linux-5.4.158/kernel/printk/printk.c    2021-11-06 
13:59:45.000000000 +0100//
//+++ linux-5.4.159/kernel/printk/printk.c    2021-11-12 
14:43:05.000000000 +0100//
//@@ -2193,8 +2193,15 @@//
//     char *s, *options, *brl_options = NULL;//
//     int idx;//
////
//-    if (str[0] == 0)//
//+    /*//
//+     * console="" or console=null have been suggested as a way to//
//+     * disable console output. Use ttynull that has been created//
//+     * for exacly this purpose.//
//+     *///
//+    if (str[0] == 0 || strcmp(str, "null") == 0) {//
//+        __add_preferred_console("ttynull", 0, NULL, NULL);//
//         return 1;//
//+    }//
////
//     if (_braille_console_setup(&str, &brl_options))//
//         return 1;/

I checked my kernelconfig and found that I have no ttynull device 
configured (/CONFIG_NULL_TTY=n/). Add /CONFIG_NULL_TTY=y/ to my 
kernelconfig doesn't made a change.

When I undo the change above, everything works fine.


Does anybody know, what could be the main trigger for the error above?


Regards,

Sarah



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