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/init.h>
   5
   6 #include <asm/dcc.h>
   7 #include <asm/processor.h>
   8
   9 #include "hvc_console.h"
  10
  11 /* DCC Status Bits */
  12 #define DCC_STATUS_RX           (1 << 30)
  13 #define DCC_STATUS_TX           (1 << 29)
  14
  15 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
  16 {
  17         int i;
  18
  19         for (i = 0; i < count; i++) {
  20                 while (__dcc_getstatus() & DCC_STATUS_TX)
  21                         cpu_relax();
  22
  23                 __dcc_putchar(buf[i]);
  24         }
  25
  26         return count;
  27 }
  28
  29 static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
  30 {
  31         int i;
  32
  33         for (i = 0; i < count; ++i)
  34                 if (__dcc_getstatus() & DCC_STATUS_RX)
  35                         buf[i] = __dcc_getchar();
  36                 else
  37                         break;
  38
  39         return i;
  40 }
  41
  42 static bool hvc_dcc_check(void)
  43 {
  44         unsigned long time = jiffies + (HZ / 10);
  45
  46         /* Write a test character to check if it is handled */
  47         __dcc_putchar('\n');
  48
  49         while (time_is_after_jiffies(time)) {
  50                 if (!(__dcc_getstatus() & DCC_STATUS_TX))
  51                         return true;
  52         }
  53
  54         return false;
  55 }
  56
  57 static const struct hv_ops hvc_dcc_get_put_ops = {
  58         .get_chars = hvc_dcc_get_chars,
  59         .put_chars = hvc_dcc_put_chars,
  60 };
  61
  62 static int __init hvc_dcc_console_init(void)
  63 {
  64         int ret;
  65
  66         if (!hvc_dcc_check())
  67                 return -ENODEV;
  68
  69         /* Returns -1 if error */
  70         ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
  71
  72         return ret < 0 ? -ENODEV : 0;
  73 }
  74 console_initcall(hvc_dcc_console_init);
  75
  76 static int __init hvc_dcc_init(void)
  77 {
  78         struct hvc_struct *p;
  79
  80         if (!hvc_dcc_check())
  81                 return -ENODEV;
  82
  83         p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
  84
  85         return PTR_ERR_OR_ZERO(p);
  86 }
  87 device_initcall(hvc_dcc_init);