drivers/tty/hvc/hvc_dcc.c

   1 /* Copyright (c) 2010, 2014 The Linux Foundation. All rights reserved.
   2  *
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License version 2 and
   5  * only version 2 as published by the Free Software Foundation.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  */
  12
  13 #include <linux/init.h>
  14
  15 #include <asm/dcc.h>
  16 #include <asm/processor.h>
  17
  18 #include "hvc_console.h"
  19
  20 /* DCC Status Bits */
  21 #define DCC_STATUS_RX           (1 << 30)
  22 #define DCC_STATUS_TX           (1 << 29)
  23
  24 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
  25 {
  26         int i;
  27
  28         for (i = 0; i < count; i++) {
  29                 while (__dcc_getstatus() & DCC_STATUS_TX)
  30                         cpu_relax();
  31
  32                 __dcc_putchar(buf[i]);
  33         }
  34
  35         return count;
  36 }
  37
  38 static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
  39 {
  40         int i;
  41
  42         for (i = 0; i < count; ++i)
  43                 if (__dcc_getstatus() & DCC_STATUS_RX)
  44                         buf[i] = __dcc_getchar();
  45                 else
  46                         break;
  47
  48         return i;
  49 }
  50
  51 static bool hvc_dcc_check(void)
  52 {
  53         unsigned long time = jiffies + (HZ / 10);
  54
  55         /* Write a test character to check if it is handled */
  56         __dcc_putchar('\n');
  57
  58         while (time_is_after_jiffies(time)) {
  59                 if (!(__dcc_getstatus() & DCC_STATUS_TX))
  60                         return true;
  61         }
  62
  63         return false;
  64 }
  65
  66 static const struct hv_ops hvc_dcc_get_put_ops = {
  67         .get_chars = hvc_dcc_get_chars,
  68         .put_chars = hvc_dcc_put_chars,
  69 };
  70
  71 static int __init hvc_dcc_console_init(void)
  72 {
  73         int ret;
  74
  75         if (!hvc_dcc_check())
  76                 return -ENODEV;
  77
  78         /* Returns -1 if error */
  79         ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
  80
  81         return ret < 0 ? -ENODEV : 0;
  82 }
  83 console_initcall(hvc_dcc_console_init);
  84
  85 static int __init hvc_dcc_init(void)
  86 {
  87         struct hvc_struct *p;
  88
  89         if (!hvc_dcc_check())
  90                 return -ENODEV;
  91
  92         p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
  93
  94         return PTR_ERR_OR_ZERO(p);
  95 }
  96 device_initcall(hvc_dcc_init);