arch/arm64/include/asm/dcc.h

   1 /* Copyright (c) 2014-2015 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  * A call to __dcc_getchar() or __dcc_putchar() is typically followed by
  13  * a call to __dcc_getstatus().  We want to make sure that the CPU does
  14  * not speculative read the DCC status before executing the read or write
  15  * instruction.  That's what the ISBs are for.
  16  *
  17  * The 'volatile' ensures that the compiler does not cache the status bits,
  18  * and instead reads the DCC register every time.
  19  */
  20 #ifndef __ASM_DCC_H
  21 #define __ASM_DCC_H
  22
  23 #include <asm/barrier.h>
  24 #include <asm/sysreg.h>
  25
  26 static inline u32 __dcc_getstatus(void)
  27 {
  28         return read_sysreg(mdccsr_el0);
  29 }
  30
  31 static inline char __dcc_getchar(void)
  32 {
  33         char c = read_sysreg(dbgdtrrx_el0);
  34         isb();
  35
  36         return c;
  37 }
  38
  39 static inline void __dcc_putchar(char c)
  40 {
  41         /*
  42          * The typecast is to make absolutely certain that 'c' is
  43          * zero-extended.
  44          */
  45         write_sysreg((unsigned char)c, dbgdtrtx_el0);
  46         isb();
  47 }
  48
  49 #endif