earlycon.c

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#include <core/system.h>
#include <console/earlycon.h>
#include <cpu/io.h>
#include <platform/virt.h>
 
/* The PL011's registers: data, and flags. */
#define UART_DR     0x00    /* data */
#define UART_FR     0x18    /* flags */
#define UART_FR_TXFF  (1 << 5)  /* the transmit FIFO is full */
 
static uintptr_t uart = VIRT_REG(VIRT_UART);
 
/*
 * Writes a character to the UART, waiting while its FIFO is full; a
 * newline is sent as CR LF. The wait is bounded, so that a UART that
 * never takes the character doesn't hang the kernel.
 */
int earlycon_putc(char c)
{
    if (c == '\n')
        earlycon_putc('\r');
 
    for (int i = 0; i < 100000 && (mmio_read32(uart + UART_FR) & UART_FR_TXFF); ++i)
        ;
 
    mmio_write32(uart + UART_DR, (uint8_t) c);
    return 1;
}
 
/*
 * Writes a string to the UART.
 */
int earlycon_puts(char *s)
{
    int n = 0;
 
    while (*s)
        n += earlycon_putc(*s++);
 
    return n;
}
 
/*
 * Says whether the early console is on the screen: it isn't, it's the
 * serial port.
 */
int earlycon_on_screen(void)
{
    return 0;
}
 
/* Sets up the early console. QEMU's PL011 needs no setup: it's on, at
 * any speed. */
void earlycon_init(void)
{
}
 
/* Sets up the early console again, once the command line is read:
 * nothing to do. */
void earlycon_reinit(void)
{
}