Re: [PATCH v11 4/5] x86/earlyprintk: setup earlyprintk as early as possible

Andy Shevchenko
2015-06-09T17:01:06Z

On Tue, 2015-06-09 at 17:11 +0600, Alexander Kuleshov wrote:
> 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 the 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.
>
> It provides earlyprintk only for serial console, because other needs in
> ioremap which is not initialized yet.
>
> Tested it with qemu and real hardware, so early_printk() is usable and
> prints to serial console right after setup_early_printk function called.
>

One topic to discuss below.

> Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
> ---
> arch/x86/include/asm/setup.h | 6 ++++++
> arch/x86/kernel/early_printk.c | 33 ++++++++++++++++++++++++++++++---
> arch/x86/kernel/head32.c | 3 +++
> arch/x86/kernel/head64.c | 5 ++++-
> 4 files changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
> index 59efd0d..180bda4 100644
> --- a/arch/x86/include/asm/setup.h
> +++ b/arch/x86/include/asm/setup.h
> @@ -120,0 +120,0 @@ asmlinkage void __init x86_64_start_reservations(char *real_mode_data);
>
> #endif /* __i386__ */
> void __init setup_builtin_cmdline(void);
> +#ifdef CONFIG_EARLY_PRINTK
> +/* used by arch/x86/kernel/head{32,64}.c */
> +extern int __init setup_early_serial_console(void);
> +#else
> +static inline int __init setup_early_serial_console(void) { return 0; }
> +#endif /* CONFIG_EARLY_PRINTK */
> #endif /* _SETUP */
> #else
> #define RESERVE_BRK(name,sz) \
> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> index 89427d8..6442cd2 100644
> --- a/arch/x86/kernel/early_printk.c
> +++ b/arch/x86/kernel/early_printk.c
> @@ -342,19 +342,22 @@ 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);
> }
> #ifdef CONFIG_PCI
> - if (!strncmp(buf, "pciserial", 9)) {
> + if (!strncmp(buf, "pciserial", 9) &&
> + early_serial_console.index == -1) {
> early_pci_serial_init(buf + 9);
> early_console_register(&early_serial_console, keep);
> buf += 9; /* Keep from match the above "serial" */
> @@ -385,4 +388,28 @@ static int __init setup_early_printk(char *buf)
> return 0;
> }
>
> +int __init setup_early_serial_console(void)
> +{
> + 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);
> +}

I'm still not convincing by this code to be in that form and here. What
about to refactor setup_early_printk() to helper which will do parse
parameters to a let say structure where one of the flag will be
struct early_printk_param {
…
const char *arg;
bool serial;
}

Your function will be something like this

struct early_printk_param epp;

parse_early_printk_param(&epp);

if (!epp->serial)
return /* whatever error code */;

return setup_early_printk(epp.arg);

> +
> early_param("earlyprintk", setup_early_printk);
> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
> index f28d10f..908ee47 100644
> --- a/arch/x86/kernel/head32.c
> +++ b/arch/x86/kernel/head32.c
> @@ -38,0 +38,0 @@ asmlinkage __visible void __init i386_start_kernel(void)
> /* Allocate early log buffer */
> setup_log_buf(1);
>
> + setup_early_serial_console();
> + early_printk("Early printk is initialized\n");
> +
> cr4_init_shadow();
> sanitize_boot_params(&boot_params);
>
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 53662d2..041be2c 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -176,0 +176,0 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>
> /* Allocate early log buffer */
> setup_log_buf(1);
>
> + setup_early_serial_console();
> + early_printk("Early printk is initialized\n");
> +
> /*
> * Load microcode early on BSP.
> */

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