sifive-uart.c 2.5 KB

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  1. /*
  2. * SPDX-License-Identifier: BSD-2-Clause
  3. *
  4. * Copyright (c) 2019 Western Digital Corporation or its affiliates.
  5. *
  6. * Authors:
  7. * Anup Patel <anup.patel@wdc.com>
  8. */
  9. #include <sbi/riscv_io.h>
  10. #include <sbi/sbi_console.h>
  11. #include <sbi_utils/serial/sifive-uart.h>
  12. /* clang-format off */
  13. #define UART_REG_TXFIFO 0
  14. #define UART_REG_RXFIFO 1
  15. #define UART_REG_TXCTRL 2
  16. #define UART_REG_RXCTRL 3
  17. #define UART_REG_IE 4
  18. #define UART_REG_IP 5
  19. #define UART_REG_DIV 6
  20. #define UART_TXFIFO_FULL 0x80000000
  21. #define UART_RXFIFO_EMPTY 0x80000000
  22. #define UART_RXFIFO_DATA 0x000000ff
  23. #define UART_TXCTRL_TXEN 0x1
  24. #define UART_RXCTRL_RXEN 0x1
  25. /* clang-format on */
  26. static volatile char *uart_base;
  27. static u32 uart_in_freq;
  28. static u32 uart_baudrate;
  29. /**
  30. * Find minimum divisor divides in_freq to max_target_hz;
  31. * Based on uart driver n SiFive FSBL.
  32. *
  33. * f_baud = f_in / (div + 1) => div = (f_in / f_baud) - 1
  34. * The nearest integer solution requires rounding up as to not exceed max_target_hz.
  35. * div = ceil(f_in / f_baud) - 1
  36. * = floor((f_in - 1 + f_baud) / f_baud) - 1
  37. * This should not overflow as long as (f_in - 1 + f_baud) does not exceed
  38. * 2^32 - 1, which is unlikely since we represent frequencies in kHz.
  39. */
  40. static inline unsigned int uart_min_clk_divisor(uint64_t in_freq,
  41. uint64_t max_target_hz)
  42. {
  43. uint64_t quotient = (in_freq + max_target_hz - 1) / (max_target_hz);
  44. /* Avoid underflow */
  45. if (quotient == 0)
  46. return 0;
  47. else
  48. return quotient - 1;
  49. }
  50. static u32 get_reg(u32 num)
  51. {
  52. return readl(uart_base + (num * 0x4));
  53. }
  54. static void set_reg(u32 num, u32 val)
  55. {
  56. writel(val, uart_base + (num * 0x4));
  57. }
  58. static void sifive_uart_putc(char ch)
  59. {
  60. while (get_reg(UART_REG_TXFIFO) & UART_TXFIFO_FULL)
  61. ;
  62. set_reg(UART_REG_TXFIFO, ch);
  63. }
  64. static int sifive_uart_getc(void)
  65. {
  66. u32 ret = get_reg(UART_REG_RXFIFO);
  67. if (!(ret & UART_RXFIFO_EMPTY))
  68. return ret & UART_RXFIFO_DATA;
  69. return -1;
  70. }
  71. static struct sbi_console_device sifive_console = {
  72. .name = "sifive_uart",
  73. .console_putc = sifive_uart_putc,
  74. .console_getc = sifive_uart_getc
  75. };
  76. int sifive_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
  77. {
  78. uart_base = (volatile char *)base;
  79. uart_in_freq = in_freq;
  80. uart_baudrate = baudrate;
  81. /* Configure baudrate */
  82. if (in_freq && baudrate)
  83. set_reg(UART_REG_DIV, uart_min_clk_divisor(in_freq, baudrate));
  84. /* Disable interrupts */
  85. set_reg(UART_REG_IE, 0);
  86. /* Enable TX */
  87. set_reg(UART_REG_TXCTRL, UART_TXCTRL_TXEN);
  88. /* Enable Rx */
  89. set_reg(UART_REG_RXCTRL, UART_RXCTRL_RXEN);
  90. sbi_console_set_device(&sifive_console);
  91. return 0;
  92. }