drivers/tty/hvc/hvc_dcc.c

   1 /* Copyright (c) 2010, Code Aurora Forum. 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  * You should have received a copy of the GNU General Public License
  13  * along with this program; if not, write to the Free Software
  14  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  15  * 02110-1301, USA.
  16  */
  17
  18 #include <linux/console.h>
  19 #include <linux/delay.h>
  20 #include <linux/err.h>
  21 #include <linux/init.h>
  22 #include <linux/moduleparam.h>
  23 #include <linux/types.h>
  24
  25 #include <asm/processor.h>
  26
  27 #include "hvc_console.h"
  28
  29 /* DCC Status Bits */
  30 #define DCC_STATUS_RX           (1 << 30)
  31 #define DCC_STATUS_TX           (1 << 29)
  32
  33 static inline u32 __dcc_getstatus(void)
  34 {
  35         u32 __ret;
  36         asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
  37                 : "=r" (__ret) : : "cc");
  38
  39         return __ret;
  40 }
  41
  42
  43 static inline char __dcc_getchar(void)
  44 {
  45         char __c;
  46
  47         asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
  48                 : "=r" (__c));
  49         isb();
  50
  51         return __c;
  52 }
  53
  54 static inline void __dcc_putchar(char c)
  55 {
  56         asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char"
  57                 : /* no output register */
  58                 : "r" (c));
  59         isb();
  60 }
  61
  62 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
  63 {
  64         int i;
  65
  66         for (i = 0; i < count; i++) {
  67                 while (__dcc_getstatus() & DCC_STATUS_TX)
  68                         cpu_relax();
  69
  70                 __dcc_putchar(buf[i]);
  71         }
  72
  73         return count;
  74 }
  75
  76 static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
  77 {
  78         int i;
  79
  80         for (i = 0; i < count; ++i)
  81                 if (__dcc_getstatus() & DCC_STATUS_RX)
  82                         buf[i] = __dcc_getchar();
  83                 else
  84                         break;
  85
  86         return i;
  87 }
  88
  89 static bool hvc_dcc_check(void)
  90 {
  91         unsigned long time = jiffies + (HZ / 10);
  92
  93         /* Write a test character to check if it is handled */
  94         __dcc_putchar('\n');
  95
  96         while (time_is_after_jiffies(time)) {
  97                 if (!(__dcc_getstatus() & DCC_STATUS_TX))
  98                         return true;
  99         }
 100
 101         return false;
 102 }
 103
 104 static const struct hv_ops hvc_dcc_get_put_ops = {
 105         .get_chars = hvc_dcc_get_chars,
 106         .put_chars = hvc_dcc_put_chars,
 107 };
 108
 109 static int __init hvc_dcc_console_init(void)
 110 {
 111         if (!hvc_dcc_check())
 112                 return -ENODEV;
 113
 114         hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
 115         return 0;
 116 }
 117 console_initcall(hvc_dcc_console_init);
 118
 119 static int __init hvc_dcc_init(void)
 120 {
 121         if (!hvc_dcc_check())
 122                 return -ENODEV;
 123
 124         hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
 125         return 0;
 126 }
 127 device_initcall(hvc_dcc_init);