[PATCH 2/2 v4] x86/earlyprintk: setup earlyprintk as early as possible

Alexander Kuleshov
2015-04-09T08:19:20Z

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 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 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 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.

Changes v2->v3:

* Call setup_cmdline before setup_early_printk;
* setup_early_printk call wrapped with the setup_early_serial_console which
checks that 'serial' given to the earlyprintk command line option. This
prevents call of the setup_early_printk with the given pciserial/dbgp/efi,
because they are using early_ioremap.

Changes v3->v4:

* Move setup_early_serial_console from the include/linux/printk.h
to the arch/x86/include/asm/serial.h, because this function is only
for x86 now.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
---
arch/x86/include/asm/serial.h | 7 +++++++
arch/x86/kernel/early_printk.c | 31 +++++++++++++++++++++++++++++--
arch/x86/kernel/head32.c | 5 +++++
arch/x86/kernel/head64.c | 9 ++++++++-
4 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/serial.h b/arch/x86/include/asm/serial.h
index 460b84f..789e123 100644
--- a/arch/x86/include/asm/serial.h
+++ b/arch/x86/include/asm/serial.h
@@ -26,4 +26,11 @@
{ .uart = 0, BASE_BAUD, 0x3E8, 4, STD_COMX_FLAGS }, /* ttyS2 */ \
{ .uart = 0, BASE_BAUD, 0x2E8, 3, STD_COM4_FLAGS }, /* ttyS3 */

+
+#ifdef CONFIG_EARLY_PRINTK
+int setup_early_serial_console(void);
+#else
+static void setup_early_serial_console(void) {};
+#endif
+
#endif /* _ASM_X86_SERIAL_H */
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index a62536a..6052eba 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -11,6 +11,7 @@
#include <asm/processor.h>
#include <asm/fcntl.h>
#include <asm/setup.h>
+#include <asm/serial.h>
#include <xen/hvc-console.h>
#include <asm/pci-direct.h>
#include <asm/fixmap.h>
@@ -342,14 +343,16 @@ static int __init setup_early_printk(char *buf)
keep = (strstr(buf, "keep") != NULL);

while (*buf != '\0') {
- if (!strncmp(buf, "serial", 6)) {
+ if (!strncmp(buf, "serial", 6) &&
+ early_serial_console.index == -1) {
buf += 6;
early_serial_init(buf);
early_console_register(&early_serial_console, keep);
if (!strncmp(buf, ",ttyS", 5))
buf += 5;
}
- if (!strncmp(buf, "ttyS", 4)) {
+ if (!strncmp(buf, "ttyS", 4) &&
+ early_serial_console.index == -1) {
early_serial_init(buf + 4);
early_console_register(&early_serial_console, keep);
}
@@ -391,4 +394,28 @@ static int __init setup_early_printk(char *buf)
return 0;
}

+int setup_early_serial_console() {
+#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 7ad0ad0..c59afe4 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -19,6 +19,7 @@
#include <asm/bios_ebda.h>
#include <asm/tlbflush.h>
#include <asm/bootparam_utils.h>
+#include <asm/serial.h>

static void __init i386_default_early_setup(void)
{
@@ -32,6 +33,10 @@ static void __init i386_default_early_setup(void)
asmlinkage __visible void __init i386_start_kernel(void)
{
setup_cmdline();
+ /* setup serial console as early as possible */
+ setup_early_serial_console();
+ early_printk("Early serial console is active\n");
+
cr4_init_shadow();
sanitize_boot_params(&boot_params);

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 6eea2de..129acc3 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.
@@ -172,12 +173,16 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

copy_bootdata(__va(real_mode_data));
setup_cmdline();
+ /* setup serial console as early as possible */
+ setup_early_serial_console();
+ early_printk("Early serial console is active\n");

/*
* Load microcode early on BSP.
*/
load_ucode_bsp();

+
if (console_loglevel >= CONSOLE_LOGLEVEL_DEBUG)
early_printk("Kernel alive\n");

@@ -193,8 +198,10 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
void __init x86_64_start_reservations(char *real_mode_data)
{
/* version is always not zero if it is copied */
- if (!boot_params.hdr.version)
+ if (!boot_params.hdr.version) {
copy_bootdata(__va(real_mode_data));
+ setup_early_serial_console();
+ }

reserve_ebda_region();

--
2.3.3.611.g09038fc.dirty