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 42