Fixes and cleanups for earlyprintk aka boot console

The console subsystem already has an idea of a boot console, using the
CON_BOOT flag.  The implementation has some flaws though.  The major
problem is that presence of a boot console makes register_console() ignore
any other console devices (unless explicitly specified on the kernel
command line).

This patch fixes the console selection code to *not* consider a boot
console a full-featured one, so the first non-boot console registering will
become the default console instead.  This way the unregister call for the
boot console in the register_console() function actually triggers and the
handover from the boot console to the real console device works smoothly.
Added a printk for the handover, so you know which console device the
output goes to when the boot console stops printing messages.

The disable_early_printk() call is obsolete with that patch, explicitly
disabling the early console isn't needed any more as it works automagically
with that patch.

I've walked through the tree, dropped all disable_early_printk() instances
found below arch/ and tagged the consoles with CON_BOOT if needed.  The
code is tested on x86, sh (thanks to Paul) and mips (thanks to Ralf).

Changes to last version: Rediffed against -rc3, adapted to mips cleanups by
Ralf, fixed "udbg-immortal" cmd line arg on powerpc.

Signed-off-by: Gerd Hoffmann <kraxel@exsuse.de>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Andi Kleen <ak@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 10 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 4b47e59248df..c4c5a29a7bed 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -931,8 +931,16 @@ void register_console(struct console *console)
 {
         int i;
         unsigned long flags;
+        struct console *bootconsole = NULL;
 
-        if (preferred_console < 0)
+        if (console_drivers) {
+                if (console->flags & CON_BOOT)
+                        return;
+                if (console_drivers->flags & CON_BOOT)
+                        bootconsole = console_drivers;
+        }
+
+        if (preferred_console < 0 || bootconsole || !console_drivers)
                 preferred_console = selected_console;
 
         /*
@@ -978,8 +986,11 @@ void register_console(struct console *console)
         if (!(console->flags & CON_ENABLED))
                 return;
 
-        if (console_drivers && (console_drivers->flags & CON_BOOT)) {
-                unregister_console(console_drivers);
+        if (bootconsole) {
+                printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
+                       bootconsole->name, bootconsole->index,
+                       console->name, console->index);
+                unregister_console(bootconsole);
                 console->flags &= ~CON_PRINTBUFFER;
         }
 
@@ -1030,16 +1041,11 @@ int unregister_console(struct console *console)
                 }
         }
 
-        /* If last console is removed, we re-enable picking the first
-         * one that gets registered. Without that, pmac early boot console
-         * would prevent fbcon from taking over.
-         *
+        /*
          * If this isn't the last console and it has CON_CONSDEV set, we
          * need to set it on the next preferred console.
          */
-        if (console_drivers == NULL)
-                preferred_console = selected_console;
-        else if (console->flags & CON_CONSDEV)
+        if (console_drivers != NULL && console->flags & CON_CONSDEV)
                 console_drivers->flags |= CON_CONSDEV;
 
         release_console_sem();