Resguardo inicial

linux-7.2.3/arch/mips/kernel/early_printk_8250.c

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+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  8250/16550-type serial ports prom_putchar()
+ *
+ *  Copyright (C) 2010  Yoichi Yuasa <yuasa@linux-mips.org>
+ */
+#include <linux/io.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <asm/setup.h>
+
+static void __iomem *serial8250_base;
+static unsigned int serial8250_reg_shift;
+static unsigned int serial8250_tx_timeout;
+
+void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
+				  unsigned int timeout)
+{
+	serial8250_base = (void __iomem *)base;
+	serial8250_reg_shift = reg_shift;
+	serial8250_tx_timeout = timeout;
+}
+
+static inline u8 serial_in(int offset)
+{
+	return readb(serial8250_base + (offset << serial8250_reg_shift));
+}
+
+static inline void serial_out(int offset, char value)
+{
+	writeb(value, serial8250_base + (offset << serial8250_reg_shift));
+}
+
+void prom_putchar(char c)
+{
+	unsigned int timeout;
+	int status, bits;
+
+	if (!serial8250_base)
+		return;
+
+	timeout = serial8250_tx_timeout;
+	bits = UART_LSR_TEMT | UART_LSR_THRE;
+
+	do {
+		status = serial_in(UART_LSR);
+
+		if (--timeout == 0)
+			break;
+	} while ((status & bits) != bits);
+
+	if (timeout)
+		serial_out(UART_TX, c);
+}