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Date: Sat, 10 Jul 2010 13:49:23 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: Pekka Enberg <penberg@...helsinki.fi>
CC: hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org,
Cyrill Gorcunov <gorcunov@...il.com>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2] x86: Early-boot serial I/O support
On 07/10/2010 12:40 PM, Pekka Enberg wrote:
> This patch adds serial I/O support to very early boot printf(). It's useful for
> debugging boot code when running Linux under KVM, for example. The actual code
> was lifted from early printk.
>
> Cc: Cyrill Gorcunov <gorcunov@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
> ---
> v1 -> v2:
>
> - Use 'earlyprintk' kernel parameter to determine whether to use
> early serial or not as suggested by Yinghai and hpa.
>
> arch/x86/boot/boot.h | 16 +++++++
> arch/x86/boot/main.c | 3 +
> arch/x86/boot/string.c | 41 ++++++++++++++++++
> arch/x86/boot/tty.c | 111 +++++++++++++++++++++++++++++++++++++++++++++---
> 4 files changed, 165 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
> index 98239d2..f05b5ac 100644
> --- a/arch/x86/boot/boot.h
> +++ b/arch/x86/boot/boot.h
> @@ -37,6 +37,8 @@
> extern struct setup_header hdr;
> extern struct boot_params boot_params;
>
> +#define cpu_relax() asm volatile("rep; nop" ::: "memory")
> +
> /* Basic port I/O */
> static inline void outb(u8 v, u16 port)
> {
> @@ -203,6 +205,17 @@ static inline int isdigit(int ch)
> return (ch >= '0') && (ch <= '9');
> }
>
> +static inline int isxdigit(int ch)
> +{
> + if (isdigit(ch))
> + return true;
> +
> + if ((ch >= 'a') && (ch <= 'f'))
> + return true;
> +
> + return (ch >= 'A') && (ch <= 'F');
> +}
> +
> /* Heap -- available for dynamic lists. */
> extern char _end[];
> extern char *HEAP;
> @@ -329,10 +342,13 @@ void initregs(struct biosregs *regs);
>
> /* string.c */
> int strcmp(const char *str1, const char *str2);
> +int strncmp(const char *cs, const char *ct, size_t count);
> size_t strnlen(const char *s, size_t maxlen);
> unsigned int atou(const char *s);
> +unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base);
>
> /* tty.c */
> +void console_init(void);
> void puts(const char *);
> void putchar(int);
> int getchar(void);
> diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
> index 140172b..4ef1a33 100644
> --- a/arch/x86/boot/main.c
> +++ b/arch/x86/boot/main.c
> @@ -130,6 +130,9 @@ void main(void)
> /* First, copy the boot header into the "zeropage" */
> copy_boot_params();
>
> + /* Initialize the early-boot console */
> + console_init();
> +
> /* End of heap check */
> init_heap();
>
> diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
> index f94b7a0..aba29df 100644
> --- a/arch/x86/boot/string.c
> +++ b/arch/x86/boot/string.c
> @@ -30,6 +30,22 @@ int strcmp(const char *str1, const char *str2)
> return 0;
> }
>
> +int strncmp(const char *cs, const char *ct, size_t count)
> +{
> + unsigned char c1, c2;
> +
> + while (count) {
> + c1 = *cs++;
> + c2 = *ct++;
> + if (c1 != c2)
> + return c1 < c2 ? -1 : 1;
> + if (!c1)
> + break;
> + count--;
> + }
> + return 0;
> +}
> +
> size_t strnlen(const char *s, size_t maxlen)
> {
> const char *es = s;
> @@ -48,3 +64,28 @@ unsigned int atou(const char *s)
> i = i * 10 + (*s++ - '0');
> return i;
> }
> +
> +/* Works only for digits and letters, but small and fast */
> +#define TOLOWER(x) ((x) | 0x20)
> +
> +unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
> +{
> + unsigned long long result = 0;
> +
> + if (base == 16 && cp[0] == '0' && TOLOWER(cp[1]) == 'x')
> + cp += 2;
> +
> + while (isxdigit(*cp)) {
> + unsigned int value;
> +
> + value = isdigit(*cp) ? *cp - '0' : TOLOWER(*cp) - 'a' + 10;
> + if (value >= base)
> + break;
> + result = result * base + value;
> + cp++;
> + }
> + if (endp)
> + *endp = (char *)cp;
> +
> + return result;
> +}
> diff --git a/arch/x86/boot/tty.c b/arch/x86/boot/tty.c
> index 01ec69c..f3ceee2 100644
> --- a/arch/x86/boot/tty.c
> +++ b/arch/x86/boot/tty.c
> @@ -10,23 +10,51 @@
> * ----------------------------------------------------------------------- */
>
> /*
> - * Very simple screen I/O
> - * XXX: Probably should add very simple serial I/O?
> + * Very simple screen and serial I/O
> */
>
> #include "boot.h"
>
> +#define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
> +
> +static int early_serial_base;
> +
> +#define XMTRDY 0x20
> +
> +#define DLAB 0x80
> +
> +#define TXR 0 /* Transmit register (WRITE) */
> +#define RXR 0 /* Receive register (READ) */
> +#define IER 1 /* Interrupt Enable */
> +#define IIR 2 /* Interrupt ID */
> +#define FCR 2 /* FIFO control */
> +#define LCR 3 /* Line control */
> +#define MCR 4 /* Modem control */
> +#define LSR 5 /* Line Status */
> +#define MSR 6 /* Modem Status */
> +#define DLL 0 /* Divisor Latch Low */
> +#define DLH 1 /* Divisor latch High */
> +
> +#define DEFAULT_BAUD 9600
> +
> /*
> * These functions are in .inittext so they can be used to signal
> * error during initialization.
> */
>
> -void __attribute__((section(".inittext"))) putchar(int ch)
> +static void __attribute__((section(".inittext"))) serial_putchar(int ch)
> {
> - struct biosregs ireg;
> + unsigned timeout = 0xffff;
>
> - if (ch == '\n')
> - putchar('\r'); /* \n -> \r\n */
> + while ((inb(early_serial_base + LSR) & XMTRDY) == 0 && --timeout)
> + cpu_relax();
> +
> + outb(ch, early_serial_base + TXR);
> +}
> +
> +static void __attribute__((section(".inittext"))) bios_putchar(int ch)
> +{
> + struct biosregs ireg;
>
> initregs(&ireg);
> ireg.bx = 0x0007;
> @@ -36,6 +64,17 @@ void __attribute__((section(".inittext"))) putchar(int ch)
> intcall(0x10, &ireg, NULL);
> }
>
> +void __attribute__((section(".inittext"))) putchar(int ch)
> +{
> + if (ch == '\n')
> + putchar('\r'); /* \n -> \r\n */
> +
> + bios_putchar(ch);
> +
> + if (early_serial_base != 0)
> + serial_putchar(ch);
> +}
> +
> void __attribute__((section(".inittext"))) puts(const char *str)
> {
> while (*str)
> @@ -112,3 +151,63 @@ int getchar_timeout(void)
>
> return 0; /* Timeout! */
> }
> +
> +static void early_serial_init(int baud)
> +{
> + unsigned char c;
> + unsigned divisor;
> +
> + outb(0x3, early_serial_base + LCR); /* 8n1 */
> + outb(0, early_serial_base + IER); /* no interrupt */
> + outb(0, early_serial_base + FCR); /* no fifo */
> + outb(0x3, early_serial_base + MCR); /* DTR + RTS */
> +
> + divisor = 115200 / baud;
> + c = inb(early_serial_base + LCR);
> + outb(c | DLAB, early_serial_base + LCR);
> + outb(divisor & 0xff, early_serial_base + DLL);
> + outb((divisor >> 8) & 0xff, early_serial_base + DLH);
> + outb(c & ~DLAB, early_serial_base + LCR);
> +}
> +
> +void console_init(void)
> +{
> + int baud = DEFAULT_BAUD;
> + char arg[32];
> + int pos = 0;
> +
> + if (cmdline_find_option("earlyprintk", arg, sizeof arg) > 0) {
> + char *e;
> +
> + if (!strncmp(arg, "serial", 6)) {
> + early_serial_base = DEFAULT_SERIAL_PORT;
> + pos += 6;
> + }
> +
> + if (arg[pos] == ',')
> + pos++;
> +
> + if (!strncmp(arg, "ttyS", 4)) {
> + static const int bases[] = { 0x3f8, 0x2f8 };
> + int port = 0;
> +
> + if (!strncmp(arg + pos, "ttyS", 4))
> + pos += 4;
> +
> + if (arg[pos++] == '1')
> + port = 1;
> +
> + early_serial_base = bases[port];
> + }
> +
> + if (arg[pos] == ',')
> + pos++;
> +
> + baud = simple_strtoull(arg + pos, &e, 0);
> + if (baud == 0 || arg + pos == e)
> + baud = DEFAULT_BAUD;
> + }
> +
> + if (early_serial_base != 0)
> + early_serial_init(baud);
> +}
can you analyze "console=uart8250,io,0x3f8,115200n8" instead?
that is equal to "earlyprintk=ttyS0,115200 console=ttyS0,115200"
so we only use one for all.
also like to kill earlyprintk=ttyS0,115200 to favor earlycon
Thanks
Yinghai
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