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 50