[PATCH v6 3/3] x86/earlyprintk: setup earlyprintk as early as possible

[Alexander Kuleshov]

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

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

Tested it with qemu, so early_printk() is usable and prints to serial
console right after setup_early_printk function called.

Signed-off-by: Alexander Kuleshov <kuleshovmail@xxxxxxxxx>
---
 arch/x86/include/asm/serial.h  |  3 +++
 arch/x86/kernel/early_printk.c | 25 +++++++++++++++++++++++++
 arch/x86/kernel/head32.c       |  5 +++++
 arch/x86/kernel/head64.c       |  5 +++++
 4 files changed, 38 insertions(+)

diff --git a/arch/x86/include/asm/serial.h b/arch/x86/include/asm/serial.h
index 8378b8c..198f041 100644
--- a/arch/x86/include/asm/serial.h
+++ b/arch/x86/include/asm/serial.h
@@ -26,4 +26,7 @@
 	{ .uart = 0,	BASE_BAUD,	0x3E8,	4,	STD_COMX_FLAGS	}, /* ttyS2 */	\
 	{ .uart = 0,	BASE_BAUD,	0x2E8,	3,	STD_COM4_FLAGS	}, /* ttyS3 */

+/* used by arch/x86/kernel/head{32,64}.c */
+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..96425c3 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 92e8b5f..d325d0c 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 38da21c..06fcc1b 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -173,6 +173,11 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	copy_bootdata(__va(real_mode_data));
 	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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