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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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f2bfdb0628
The current code waits until the transmitter becomes empty, before sending each character, and after finishing the whole string. This seems a bit redundant. It can be more efficient by checking the transmitter only after sending each character. This should be safe because the transmitter is already empty at the first entry of serial_putc(). Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
147 lines
4.2 KiB
C
147 lines
4.2 KiB
C
/*
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* Early serial console for 8250/16550 devices
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*
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* (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
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* Bjorn Helgaas <bjorn.helgaas@hp.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Based on the 8250.c serial driver, Copyright (C) 2001 Russell King,
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* and on early_printk.c by Andi Kleen.
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*
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* This is for use before the serial driver has initialized, in
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* particular, before the UARTs have been discovered and named.
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* Instead of specifying the console device as, e.g., "ttyS0",
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* we locate the device directly by its MMIO or I/O port address.
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*
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* The user can specify the device directly, e.g.,
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* earlycon=uart8250,io,0x3f8,9600n8
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* earlycon=uart8250,mmio,0xff5e0000,115200n8
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* earlycon=uart8250,mmio32,0xff5e0000,115200n8
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* or
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* console=uart8250,io,0x3f8,9600n8
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* console=uart8250,mmio,0xff5e0000,115200n8
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* console=uart8250,mmio32,0xff5e0000,115200n8
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*/
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#include <linux/tty.h>
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#include <linux/init.h>
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#include <linux/console.h>
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#include <linux/of.h>
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#include <linux/of_device.h>
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#include <linux/serial_reg.h>
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#include <linux/serial.h>
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#include <linux/serial_8250.h>
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#include <asm/io.h>
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#include <asm/serial.h>
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static unsigned int __init serial8250_early_in(struct uart_port *port, int offset)
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{
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switch (port->iotype) {
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case UPIO_MEM:
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return readb(port->membase + offset);
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case UPIO_MEM32:
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return readl(port->membase + (offset << 2));
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case UPIO_MEM32BE:
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return ioread32be(port->membase + (offset << 2));
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case UPIO_PORT:
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return inb(port->iobase + offset);
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default:
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return 0;
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}
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}
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static void __init serial8250_early_out(struct uart_port *port, int offset, int value)
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{
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switch (port->iotype) {
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case UPIO_MEM:
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writeb(value, port->membase + offset);
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break;
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case UPIO_MEM32:
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writel(value, port->membase + (offset << 2));
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break;
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case UPIO_MEM32BE:
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iowrite32be(value, port->membase + (offset << 2));
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break;
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case UPIO_PORT:
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outb(value, port->iobase + offset);
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break;
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}
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}
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#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
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static void __init wait_for_xmitr(struct uart_port *port)
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{
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unsigned int status;
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for (;;) {
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status = serial8250_early_in(port, UART_LSR);
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if ((status & BOTH_EMPTY) == BOTH_EMPTY)
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return;
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cpu_relax();
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}
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}
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static void __init serial_putc(struct uart_port *port, int c)
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{
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serial8250_early_out(port, UART_TX, c);
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wait_for_xmitr(port);
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}
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static void __init early_serial8250_write(struct console *console,
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const char *s, unsigned int count)
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{
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struct earlycon_device *device = console->data;
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struct uart_port *port = &device->port;
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uart_console_write(port, s, count, serial_putc);
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}
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static void __init init_port(struct earlycon_device *device)
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{
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struct uart_port *port = &device->port;
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unsigned int divisor;
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unsigned char c;
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unsigned int ier;
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serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */
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ier = serial8250_early_in(port, UART_IER);
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serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
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serial8250_early_out(port, UART_FCR, 0); /* no fifo */
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serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */
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divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
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c = serial8250_early_in(port, UART_LCR);
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serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
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serial8250_early_out(port, UART_DLL, divisor & 0xff);
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serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
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serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
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}
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int __init early_serial8250_setup(struct earlycon_device *device,
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const char *options)
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{
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if (!(device->port.membase || device->port.iobase))
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return -ENODEV;
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if (!device->baud) {
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struct uart_port *port = &device->port;
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unsigned int ier;
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/* assume the device was initialized, only mask interrupts */
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ier = serial8250_early_in(port, UART_IER);
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serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
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} else
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init_port(device);
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device->con->write = early_serial8250_write;
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return 0;
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}
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EARLYCON_DECLARE(uart8250, early_serial8250_setup);
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EARLYCON_DECLARE(uart, early_serial8250_setup);
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OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
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OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
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