[PATCH v5 2/2] x86/earlyprintk: setup earlyprintk as early as possible

[Alexander Kuleshov]

The early_printk function is usable after setup_early_printk will be executed. We
pass 'earlyprintk' through the kernel command line. It means that earlyprintk
will be usable only after the 'parse_early_param' will be executed. So we have
usable earlyprintk only during early boot, kernel decompression and after call
of the 'parse_early_param'.

This patch makes setup_early_printk visible for head{32,64}.c So 'early_printk'
function will be usabable after decompression of the kernel and before
parse_early_param will be called. It also safe if CONFIG_CMDLINE_BOOL
and CONFIG_CMDLINE_OVERRIDE are set, because setup_cmdline function will be
called before the setup_early_printk.

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

Signed-off-by: Alexander Kuleshov <kuleshovmail@xxxxxxxxx>
---
 arch/x86/include/asm/serial.h  |  2 ++
 arch/x86/kernel/early_printk.c | 25 +++++++++++++++++++++++++
 arch/x86/kernel/head32.c       |  5 +++++
 arch/x86/kernel/head64.c       |  8 +++++++-
 4 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/serial.h b/arch/x86/include/asm/serial.h
index 8378b8c..be3b73a 100644
--- a/arch/x86/include/asm/serial.h
+++ b/arch/x86/include/asm/serial.h
@@ -26,4 +26,6 @@
 	{ .uart = 0,	BASE_BAUD,	0x3E8,	4,	STD_COMX_FLAGS	}, /* ttyS2 */	\
 	{ .uart = 0,	BASE_BAUD,	0x2E8,	3,	STD_COM4_FLAGS	}, /* ttyS3 */
 
+int __init setup_early_serial_console(void);
+
 #endif /* _ASM_X86_SERIAL_H */
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 89427d8..d7cc0b1 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -385,4 +385,29 @@ static int __init setup_early_printk(char *buf)
 	return 0;
 }
 
+int __init setup_early_serial_console(void)
+{
+#ifdef CONFIG_EARLY_PRINTK
+	char *arg;
+
+	/*
+	 * make sure that we have:
+	 *	"serial,0x3f8,115200"
+	 *	"serial,ttyS0,115200"
+	 *	"ttyS0,115200"
+	 */
+	arg = strstr(boot_command_line, "earlyprintk=serial");
+	if (!arg)
+		arg = strstr(boot_command_line, "earlyprintk=ttyS");
+	if (!arg)
+		return -1;
+
+	arg = strstr(boot_command_line, "earlyprintk=");
+	/* += strlen("earlyprintk"); */
+	arg += 12;
+
+	return setup_early_printk(arg);
+#endif
+}
+
 early_param("earlyprintk", setup_early_printk);
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index 95eed21..e863ecc 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -32,6 +32,11 @@ static void __init i386_default_early_setup(void)
 asmlinkage __visible void __init i386_start_kernel(void)
 {
         setup_builtin_cmdline();
+        setup_early_serial_console();
+
+	if (console_loglevel >= CONSOLE_LOGLEVEL_DEBUG)
+                early_printk("Kernel alive\n");
+
 	cr4_init_shadow();
 	sanitize_boot_params(&boot_params);
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index df290d1..905e602 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -28,6 +28,7 @@
 #include <asm/bootparam_utils.h>
 #include <asm/microcode.h>
 #include <asm/kasan.h>
+#include <asm/serial.h>
 
 /*
  * Manage page tables very early on.
@@ -171,7 +172,12 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	load_idt((const struct desc_ptr *)&idt_descr);
 
 	copy_bootdata(__va(real_mode_data));
-        setup_builtin_cmdline();
+
+	setup_builtin_cmdline();
+	setup_early_serial_console();
+
+	if (console_loglevel >= CONSOLE_LOGLEVEL_DEBUG)
+		early_printk("Kernel alive\n");
 
 	/*
 	 * Load microcode early on BSP.
-- 
2.4.0

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