1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * Copyright (c) 2017 Intel Corporation
4  */
5 
6 #include <common.h>
7 #include <dm.h>
8 #include <ns16550.h>
9 #include <serial.h>
10 
11 /*
12  * The UART clock is calculated as
13  *
14  *	UART clock = XTAL * UART_MUL / UART_DIV
15  *
16  * The baudrate is calculated as
17  *
18  *	baud rate = UART clock / UART_PS / DLAB
19  */
20 #define UART_PS		0x30
21 #define UART_MUL	0x34
22 #define UART_DIV	0x38
23 
mid_writel(struct ns16550_plat * plat,int offset,int value)24 static void mid_writel(struct ns16550_plat *plat, int offset, int value)
25 {
26 	unsigned char *addr;
27 
28 	offset *= 1 << plat->reg_shift;
29 	addr = (unsigned char *)plat->base + offset;
30 
31 	writel(value, addr + plat->reg_offset);
32 }
33 
mid_serial_probe(struct udevice * dev)34 static int mid_serial_probe(struct udevice *dev)
35 {
36 	struct ns16550_plat *plat = dev_get_plat(dev);
37 
38 	/*
39 	 * Initialize fractional divider correctly for Intel Edison
40 	 * platform.
41 	 *
42 	 * For backward compatibility we have to set initial DLAB value
43 	 * to 16 and speed to 115200 baud, where initial frequency is
44 	 * 29491200Hz, and XTAL frequency is 38.4MHz.
45 	 */
46 	mid_writel(plat, UART_MUL, 96);
47 	mid_writel(plat, UART_DIV, 125);
48 	mid_writel(plat, UART_PS, 16);
49 
50 	return ns16550_serial_probe(dev);
51 }
52 
53 static const struct udevice_id mid_serial_ids[] = {
54 	{ .compatible = "intel,mid-uart" },
55 	{}
56 };
57 
58 U_BOOT_DRIVER(serial_intel_mid) = {
59 	.name	= "serial_intel_mid",
60 	.id	= UCLASS_SERIAL,
61 	.of_match = mid_serial_ids,
62 	.of_to_plat = ns16550_serial_of_to_plat,
63 	.plat_auto	= sizeof(struct ns16550_plat),
64 	.priv_auto	= sizeof(struct ns16550),
65 	.probe	= mid_serial_probe,
66 	.ops	= &ns16550_serial_ops,
67 };
68