linux-kernel - [PATCH 1/2 v2] x86_64/earlyprintk: setup earlyprintk as early as possible

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Date:	Tue,  7 Apr 2015 17:02:20 +0600
From:	Alexander Kuleshov <kuleshovmail@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Kuleshov <kuleshovmail@...il.com>
Subject: [PATCH 1/2 v2] x86_64/earlyprintk: setup earlyprintk as early as possible

As setup_early_printk passed to the early_param, it will be usable only after
'parse_early_param' function will be called from the 'setup_arch'. So we have
earlyprintk during early boot and decompression. Next point after decompression
of the kernel where we can use early_printk is after call of the
'parse_early_param'.

This patch removes 'earlyprintk' from the early_param and setup it right after
boot data copying. So 'early_printk' function will be usabable after
decompression of the kernel and before parse_early_param will be called.

Tested it with qemu, so early_printk() is usable and prints to serial console
right after setup_early_printk function called from arch/x86/kerne/head64.c

Changes v1->v2:

* Comment added before the setup_early_printk call;
* Added information about testing to the commit message.

Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
---
 arch/x86/kernel/early_printk.c | 4 +---
 arch/x86/kernel/head64.c       | 3 +++
 include/linux/printk.h         | 1 +
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index a62536a..4b0577b 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -329,7 +329,7 @@ static inline void early_console_register(struct console *con, int keep_early)
 	register_console(early_console);
 }
 
-static int __init setup_early_printk(char *buf)
+int __init setup_early_printk(char *buf)
 {
 	int keep;
 
@@ -390,5 +390,3 @@ static int __init setup_early_printk(char *buf)
 	}
 	return 0;
 }
-
-early_param("earlyprintk", setup_early_printk);
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index c4f8d46..4034ea6 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -172,6 +172,9 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 
 	copy_bootdata(__va(real_mode_data));
 
+	/* setup earlyprintk as early as possible */
+	setup_early_printk(boot_command_line);
+
 	/*
 	 * Load microcode early on BSP.
 	 */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index baa3f97..47e3919 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -115,6 +115,7 @@ int no_printk(const char *fmt, ...)
 #ifdef CONFIG_EARLY_PRINTK
 extern asmlinkage __printf(1, 2)
 void early_printk(const char *fmt, ...);
+int setup_early_printk(char *buf);
 #else
 static inline __printf(1, 2) __cold
 void early_printk(const char *s, ...) { }
-- 
2.3.3.611.g09038fc.dirty

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