2 files changed, 21 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e9261e938f6a..c357a31411cd 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -872,6 +872,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                                If specified, z/VM IUCV HVC accepts connections
                                from listed z/VM user IDs only.
 
+        keep_bootcon    [KNL]
+                        Do not unregister boot console at start. This is only
+                        useful for debugging when something happens in the window
+                        between unregistering the boot console and initializing
+                        the real console.
+
         i2c_bus=        [HW] Override the default board specific I2C bus speed
                              or register an additional I2C bus that is not
                              registered from board initialization code.
diff --git a/kernel/printk.c b/kernel/printk.c
index 33284adb2189..2b591f252e55 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1316,6 +1316,18 @@ void console_start(struct console *console)
 }
 EXPORT_SYMBOL(console_start);
 
+static int __read_mostly keep_bootcon;
+
+static int __init keep_bootcon_setup(char *str)
+{
+        keep_bootcon = 1;
+        printk(KERN_INFO "debug: skip boot console de-registration.\n");
+
+        return 0;
+}
+
+early_param("keep_bootcon", keep_bootcon_setup);
+
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to
@@ -1463,7 +1475,9 @@ void register_console(struct console *newcon)
          * users know there might be something in the kernel's log buffer that
          * went to the bootconsole (that they do not see on the real console)
          */
-        if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
+        if (bcon &&
+            ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
+            !keep_bootcon) {
                 /* we need to iterate through twice, to make sure we print
                  * everything out, before we unregister the console(s)
                  */