drivers/tty/hvc/hvc_dcc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (c) 2010, 2014 The Linux Foundation. All rights reserved.  */
   3
   4 #include <linux/console.h>
   5 #include <linux/init.h>
   6 #include <linux/serial.h>
   7 #include <linux/serial_core.h>
   8
   9 #include <asm/dcc.h>
  10 #include <asm/processor.h>
  11
  12 #include "hvc_console.h"
  13
  14 /* DCC Status Bits */
  15 #define DCC_STATUS_RX           (1 << 30)
  16 #define DCC_STATUS_TX           (1 << 29)
  17
  18 static void dcc_uart_console_putchar(struct uart_port *port, int ch)
  19 {
  20         while (__dcc_getstatus() & DCC_STATUS_TX)
  21                 cpu_relax();
  22
  23         __dcc_putchar(ch);
  24 }
  25
  26 static void dcc_early_write(struct console *con, const char *s, unsigned n)
  27 {
  28         struct earlycon_device *dev = con->data;
  29
  30         uart_console_write(&dev->port, s, n, dcc_uart_console_putchar);
  31 }
  32
  33 static int __init dcc_early_console_setup(struct earlycon_device *device,
  34                                           const char *opt)
  35 {
  36         device->con->write = dcc_early_write;
  37
  38         return 0;
  39 }
  40
  41 EARLYCON_DECLARE(dcc, dcc_early_console_setup);
  42
  43 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
  44 {
  45         int i;
  46
  47         for (i = 0; i < count; i++) {
  48                 while (__dcc_getstatus() & DCC_STATUS_TX)
  49                         cpu_relax();
  50
  51                 __dcc_putchar(buf[i]);
  52         }
  53
  54         return count;
  55 }
  56
  57 static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
  58 {
  59         int i;
  60
  61         for (i = 0; i < count; ++i)
  62                 if (__dcc_getstatus() & DCC_STATUS_RX)
  63                         buf[i] = __dcc_getchar();
  64                 else
  65                         break;
  66
  67         return i;
  68 }
  69
  70 static bool hvc_dcc_check(void)
  71 {
  72         unsigned long time = jiffies + (HZ / 10);
  73
  74         /* Write a test character to check if it is handled */
  75         __dcc_putchar('\n');
  76
  77         while (time_is_after_jiffies(time)) {
  78                 if (!(__dcc_getstatus() & DCC_STATUS_TX))
  79                         return true;
  80         }
  81
  82         return false;
  83 }
  84
  85 static const struct hv_ops hvc_dcc_get_put_ops = {
  86         .get_chars = hvc_dcc_get_chars,
  87         .put_chars = hvc_dcc_put_chars,
  88 };
  89
  90 static int __init hvc_dcc_console_init(void)
  91 {
  92         int ret;
  93
  94         if (!hvc_dcc_check())
  95                 return -ENODEV;
  96
  97         /* Returns -1 if error */
  98         ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
  99
 100         return ret < 0 ? -ENODEV : 0;
 101 }
 102 console_initcall(hvc_dcc_console_init);
 103
 104 static int __init hvc_dcc_init(void)
 105 {
 106         struct hvc_struct *p;
 107
 108         if (!hvc_dcc_check())
 109                 return -ENODEV;
 110
 111         p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
 112
 113         return PTR_ERR_OR_ZERO(p);
 114 }
 115 device_initcall(hvc_dcc_init);