arch/arm/kernel/thumbee.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm/kernel/thumbee.c
   4  *
   5  * Copyright (C) 2008 ARM Limited
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/init.h>
  10
  11 #include <asm/cputype.h>
  12 #include <asm/system_info.h>
  13 #include <asm/thread_notify.h>
  14
  15 /*
  16  * Access to the ThumbEE Handler Base register
  17  */
  18 static inline unsigned long teehbr_read(void)
  19 {
  20         unsigned long v;
  21         asm("mrc        p14, 6, %0, c1, c0, 0\n" : "=r" (v));
  22         return v;
  23 }
  24
  25 static inline void teehbr_write(unsigned long v)
  26 {
  27         asm("mcr        p14, 6, %0, c1, c0, 0\n" : : "r" (v));
  28 }
  29
  30 static int thumbee_notifier(struct notifier_block *self, unsigned long cmd, void *t)
  31 {
  32         struct thread_info *thread = t;
  33
  34         switch (cmd) {
  35         case THREAD_NOTIFY_FLUSH:
  36                 teehbr_write(0);
  37                 break;
  38         case THREAD_NOTIFY_SWITCH:
  39                 current_thread_info()->thumbee_state = teehbr_read();
  40                 teehbr_write(thread->thumbee_state);
  41                 break;
  42         }
  43
  44         return NOTIFY_DONE;
  45 }
  46
  47 static struct notifier_block thumbee_notifier_block = {
  48         .notifier_call  = thumbee_notifier,
  49 };
  50
  51 static int __init thumbee_init(void)
  52 {
  53         unsigned long pfr0;
  54         unsigned int cpu_arch = cpu_architecture();
  55
  56         if (cpu_arch < CPU_ARCH_ARMv7)
  57                 return 0;
  58
  59         pfr0 = read_cpuid_ext(CPUID_EXT_PFR0);
  60         if ((pfr0 & 0x0000f000) != 0x00001000)
  61                 return 0;
  62
  63         pr_info("ThumbEE CPU extension supported.\n");
  64         elf_hwcap |= HWCAP_THUMBEE;
  65         thread_register_notifier(&thumbee_notifier_block);
  66
  67         return 0;
  68 }
  69
  70 late_initcall(thumbee_init);