common/console.c


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/*
 * console.c - the console dprintf writes to. two sinks: the pl011
 * PrimeCell uart every qemu virt and SBSA board carries (DDI 0183),
 * and semihosting SYS_WRITE0, the firmware service on the qemu dev
 * path. the uart is the real hardware path, semihosting the dev
 * path, the probe at init picks whichever answers.
 *
 * Copyright (c) 2026 Bradley Morgan <brads@mainlining.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include <sys/types.h>
#include <stdint.h>
#include <debug.h>
#include <semihosting.h>

/* pl011 register map, DDI 0183, offsets from the base */
#define UART_DR			0x00	/* data register */
#define UART_FR			0x18	/* flag register */
#define UART_FR_BUSY		(1 << 3)
#define UART_FR_TXFF		(1 << 5)
#define UART_IBRD		0x24
#define UART_FBRD		0x28
#define UART_LCRH		0x2c
#define UART_CR			0x30
#define UART_CR_UARTEN		(1 << 0)
#define UART_CR_TXE		(1 << 8)
#define UART_CR_RXE		(1 << 9)
#define UART_IMSC		0x38
#define UART_ICR		0x44

/*
 * 115200 8n1 at a 24 MHz reference clock. IBRD = 24e6 / (16 * 115200)
 * = 13, FBRD = int(0.6875 * 64 + 0.5) = 44.
 */
#define UART_IBRD_VAL		13
#define UART_FBRD_VAL		44

/* the base comes from the devicetree walk, the qemu default
 * only covers the dev path before the walk runs
 */
static uintptr_t pl011_base = 0x09000000UL;

void tb_console_set_pl011(uintptr_t base)
{
	if (base)
		pl011_base = base;
}

static int console_uart_ok;

static void uart_putc(char c)
{
	volatile uint32_t *fr = (volatile uint32_t *)(pl011_base + UART_FR);
	volatile uint32_t *dr = (volatile uint32_t *)(pl011_base + UART_DR);

	/* TXFF can happen mid line on slow consoles, wait it out */
	while (*fr & UART_FR_TXFF)
		;
	*dr = (uint32_t)(unsigned char)c;
}

/*
 * pl011 probe and bringup: uart off, baud divisor, fifo on, then
 * enable tx. the clock here is the qemu virt reference, a real board
 * overrides the divisors from its clock tree, that is board
 * territory, the arch part is the sequence.
 */
static int uart_init(void)
{
	volatile uint32_t *cr = (volatile uint32_t *)(pl011_base + UART_CR);
	volatile uint32_t *ibrd = (volatile uint32_t *)(pl011_base + UART_IBRD);
	volatile uint32_t *fbrd = (volatile uint32_t *)(pl011_base + UART_FBRD);
	volatile uint32_t *lcrh = (volatile uint32_t *)(pl011_base + UART_LCRH);
	volatile uint32_t *imsc = (volatile uint32_t *)(pl011_base + UART_IMSC);
	volatile uint32_t *icr = (volatile uint32_t *)(pl011_base + UART_ICR);

	/* disable, mask irq, clear pending, divisors, fifo, enable tx */
	*cr = 0;
	*imsc = 0;
	*icr = 0x7ff;
	*ibrd = UART_IBRD_VAL;
	*fbrd = UART_FBRD_VAL;
	*lcrh = (3 << 5) | (1 << 4);	/* 8n1, fifo enabled */
	*cr = UART_CR_UARTEN | UART_CR_TXE | UART_CR_RXE;

	/* self test write, TXFF clearing means the uart answers */
	uart_putc('\0');
	while (*(volatile uint32_t *)(pl011_base + UART_FR) & UART_FR_BUSY)
		;

	return 0;
}

/*
 * lk's _dprintf sink. printf buffers a line here then hands it to
 * the sink, semihosting wants zero terminated strings not counts.
 */
#define TB_CONSOLE_MAX	256

static char console_buf[TB_CONSOLE_MAX];
static size_t console_len;

static void console_flush(void)
{
	size_t i;

	if (console_len == 0)
		return;

	if (console_uart_ok) {
		for (i = 0; i < console_len; i++)
			uart_putc(console_buf[i]);
	} else {
		console_buf[console_len] = '\0';
		smh_write0(console_buf);
	}
	console_len = 0;
}

void _putchar(char c)
{
	if (console_len >= TB_CONSOLE_MAX - 1)
		console_flush();
	if (c == '\n') {
		/* terminals want cr lf, not lf alone */
		console_buf[console_len++] = '\r';
	}
	console_buf[console_len++] = c;
	if (c == '\n')
		console_flush();
}

int tb_console_init(void)
{
	/*
	 * try the uart first, real hardware. semihosting is the qemu
	 * dev path, SYS_GET_ERRNO with nothing open, a host answers,
	 * bare metal ignores the trap.
	 */
	uart_init();
	console_uart_ok = 1;
	console_len = 0;
	(void)smh_probe();
	return 0;
}