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    SubjectRe: [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@gmail.com>
    > Cc: Ingo Molnar <mingo@redhat.com>
    > Cc: Yinghai Lu <yinghai@kernel.org>
    > Signed-off-by: Pekka Enberg <penberg@cs.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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