arch/arm64/include/asm/dcc.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /* Copyright (c) 2014-2015 The Linux Foundation. All rights reserved.
   3  *
   4  * A call to __dcc_getchar() or __dcc_putchar() is typically followed by
   5  * a call to __dcc_getstatus().  We want to make sure that the CPU does
   6  * not speculative read the DCC status before executing the read or write
   7  * instruction.  That's what the ISBs are for.
   8  *
   9  * The 'volatile' ensures that the compiler does not cache the status bits,
  10  * and instead reads the DCC register every time.
  11  */
  12 #ifndef __ASM_DCC_H
  13 #define __ASM_DCC_H
  14
  15 #include <asm/barrier.h>
  16 #include <asm/sysreg.h>
  17
  18 static inline u32 __dcc_getstatus(void)
  19 {
  20         return read_sysreg(mdccsr_el0);
  21 }
  22
  23 static inline char __dcc_getchar(void)
  24 {
  25         char c = read_sysreg(dbgdtrrx_el0);
  26         isb();
  27
  28         return c;
  29 }
  30
  31 static inline void __dcc_putchar(char c)
  32 {
  33         /*
  34          * The typecast is to make absolutely certain that 'c' is
  35          * zero-extended.
  36          */
  37         write_sysreg((unsigned char)c, dbgdtrtx_el0);
  38         isb();
  39 }
  40
  41 #endif