drivers/serial/serial_intel_mid.c

   1 /*
   2  * Copyright (c) 2017 Intel Corporation
   3  *
   4  * SPDX-License-Identifier:     GPL-2.0+
   5  */
   6
   7 #include <common.h>
   8 #include <dm.h>
   9 #include <ns16550.h>
  10 #include <serial.h>
  11
  12 /*
  13  * The UART clock is calculated as
  14  *
  15  *      UART clock = XTAL * UART_MUL / UART_DIV
  16  *
  17  * The baudrate is calculated as
  18  *
  19  *      baud rate = UART clock / UART_PS / DLAB
  20  */
  21 #define UART_PS         0x30
  22 #define UART_MUL        0x34
  23 #define UART_DIV        0x38
  24
  25 static void mid_writel(struct ns16550_platdata *plat, int offset, int value)
  26 {
  27         unsigned char *addr;
  28
  29         offset *= 1 << plat->reg_shift;
  30         addr = (unsigned char *)plat->base + offset;
  31
  32         writel(value, addr + plat->reg_offset);
  33 }
  34
  35 static int mid_serial_probe(struct udevice *dev)
  36 {
  37         struct ns16550_platdata *plat = dev_get_platdata(dev);
  38
  39         /*
  40          * Initialize fractional divider correctly for Intel Edison
  41          * platform.
  42          *
  43          * For backward compatibility we have to set initial DLAB value
  44          * to 16 and speed to 115200 baud, where initial frequency is
  45          * 29491200Hz, and XTAL frequency is 38.4MHz.
  46          */
  47         mid_writel(plat, UART_MUL, 96);
  48         mid_writel(plat, UART_DIV, 125);
  49         mid_writel(plat, UART_PS, 16);
  50
  51         return ns16550_serial_probe(dev);
  52 }
  53
  54 static const struct udevice_id mid_serial_ids[] = {
  55         { .compatible = "intel,mid-uart" },
  56         {}
  57 };
  58
  59 U_BOOT_DRIVER(serial_intel_mid) = {
  60         .name   = "serial_intel_mid",
  61         .id     = UCLASS_SERIAL,
  62         .of_match = mid_serial_ids,
  63         .ofdata_to_platdata = ns16550_serial_ofdata_to_platdata,
  64         .platdata_auto_alloc_size = sizeof(struct ns16550_platdata),
  65         .priv_auto_alloc_size = sizeof(struct NS16550),
  66         .probe  = mid_serial_probe,
  67         .ops    = &ns16550_serial_ops,
  68         .flags  = DM_FLAG_PRE_RELOC,
  69 };