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

Andy Shevchenko
2015-05-11T07:22:57Z

On Mon, 2015-05-11 at 01:14 +0600, Alexander Kuleshov wrote:
> 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 introduces setup_early_serial_console function which will search the
> 'earlyprintk' parameter in the kernel command line and setup 'earlyprintk'
> depends on result. It allows to make 'earlyprintk' 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 the
> setup_builtin_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.
>
> Changes v4->v5:
>
> * Call setup_builtin_cmdline instead of setup_cmdline

Please,
a) use back chronological order for changes,
b) put changelogs to coverletter,
c) use versioning for whole patch series (--subject-prefix is you friend
here).

>
> Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
> ---
> 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.

--
Andy Shevchenko <andriy.shevchenko@intel.com>
Intel Finland Oy