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From 8b0e42a94653d4061f0dcd88e6df9346814bd3a0 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 30 Nov 2020 01:42:09 +0106
Subject: [PATCH 108/296] printk: add console handover
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.35-rt39.tar.xz
If earlyprintk is used, a boot console will print directly to the
console immediately. The boot console will unregister itself as soon
as a non-boot console registers. However, the non-boot console does
not begin printing until its kthread has started. Since this happens
much later, there is a long pause in the console output. If the
ringbuffer is small, messages could even be dropped during the
pause.
Add a new CON_HANDOVER console flag to be used internally by printk
in order to track which non-boot console took over from a boot
console. If handover consoles have implemented write_atomic(), they
are allowed to print directly to the console until their kthread can
take over.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/console.h | 1 +
kernel/printk/printk.c | 8 +++++++-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/console.h b/include/linux/console.h
index 8b97a3e8f1ec..e6ff51883dee 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -138,6 +138,7 @@ static inline int con_debug_leave(void)
#define CON_ANYTIME (16) /* Safe to call when cpu is offline */
#define CON_BRL (32) /* Used for a braille device */
#define CON_EXTENDED (64) /* Use the extended output format a la /dev/kmsg */
+#define CON_HANDOVER (128) /* Device was previously a boot console. */
struct console {
char name[16];
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f5fd3e1671fe..18e3aabb2c5b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1727,6 +1727,8 @@ static bool console_can_sync(struct console *con)
return false;
if (con->write_atomic && kernel_sync_mode())
return true;
+ if (con->write_atomic && (con->flags & CON_HANDOVER) && !con->thread)
+ return true;
if (con->write && (con->flags & CON_BOOT) && !con->thread)
return true;
return false;
@@ -1738,6 +1740,8 @@ static bool call_sync_console_driver(struct console *con, const char *text, size
return false;
if (con->write_atomic && kernel_sync_mode())
con->write_atomic(con, text, text_len);
+ else if (con->write_atomic && (con->flags & CON_HANDOVER) && !con->thread)
+ con->write_atomic(con, text, text_len);
else if (con->write && (con->flags & CON_BOOT) && !con->thread)
con->write(con, text, text_len);
else
@@ -2823,8 +2827,10 @@ void register_console(struct console *newcon)
* the real console are the same physical device, it's annoying to
* see the beginning boot messages twice
*/
- if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
+ if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
newcon->flags &= ~CON_PRINTBUFFER;
+ newcon->flags |= CON_HANDOVER;
+ }
/*
* Put this console in the list - keep the
--
2.30.2
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