/* SPDX-License-Identifier: GPL-2.0-only */ #include <device/mmio.h> #include <boot/coreboot_tables.h> #include <console/uart.h> #include <types.h> /* * This is a driver for SiFive's own UART, documented in the FU540 manual: * https://www.sifive.com/documentation/chips/freedom-u540-c000-manual/ */ struct sifive_uart_registers { uint32_t txdata; /* Transmit data register */ uint32_t rxdata; /* Receive data register */ uint32_t txctrl; /* Transmit control register */ uint32_t rxctrl; /* Receive control register */ uint32_t ie; /* UART interrupt enable */ uint32_t ip; /* UART interrupt pending */ uint32_t div; /* Baud rate divisor */ } __packed; #define TXDATA_FULL BIT(31) #define RXDATA_EMPTY BIT(31) #define TXCTRL_TXEN BIT(0) #define TXCTRL_NSTOP_SHIFT 1 #define TXCTRL_NSTOP(x) (((x)-1) << TXCTRL_NSTOP_SHIFT) #define TXCTRL_TXCNT_SHIFT 16 #define TXCTRL_TXCNT(x) ((x) << TXCTRL_TXCNT_SHIFT) #define RXCTRL_RXEN BIT(0) #define RXCTRL_RXCNT_SHIFT 16 #define RXCTRL_RXCNT(x) ((x) << RXCTRL_RXCNT_SHIFT) #define IP_TXWM BIT(0) #define IP_RXWM BIT(1) static void sifive_uart_init(struct sifive_uart_registers *regs, int div) { /* Configure the divisor */ write32(®s->div, div); /* Enable transmission, one stop bit, transmit watermark at 1 */ write32(®s->txctrl, TXCTRL_TXEN|TXCTRL_NSTOP(1)|TXCTRL_TXCNT(1)); /* Enable reception, receive watermark at 0 */ write32(®s->rxctrl, RXCTRL_RXEN|RXCTRL_RXCNT(0)); } void uart_init(unsigned int idx) { unsigned int div; div = uart_baudrate_divisor(get_uart_baudrate(), uart_platform_refclk(), uart_input_clock_divider()); sifive_uart_init(uart_platform_baseptr(idx), div); } static bool uart_can_tx(struct sifive_uart_registers *regs) { return !(read32(®s->txdata) & TXDATA_FULL); } void uart_tx_byte(unsigned int idx, unsigned char data) { struct sifive_uart_registers *regs = uart_platform_baseptr(idx); while (!uart_can_tx(regs)) ; /* TODO: implement a timeout */ write32(®s->txdata, data); } void uart_tx_flush(unsigned int idx) { struct sifive_uart_registers *regs = uart_platform_baseptr(idx); uint32_t ip; /* Use the TX watermark bit to find out if the TX FIFO is empty */ do { ip = read32(®s->ip); } while (!(ip & IP_TXWM)); } unsigned char uart_rx_byte(unsigned int idx) { struct sifive_uart_registers *regs = uart_platform_baseptr(idx); uint32_t rxdata; do { rxdata = read32(®s->rxdata); } while (rxdata & RXDATA_EMPTY); return rxdata & 0xff; } unsigned int uart_input_clock_divider(void) { /* * The SiFive UART handles oversampling internally. The divided clock * is the baud clock. */ return 1; } void uart_fill_lb(void *data) { /* TODO */ }