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 25 static inline u32 __dcc_getstatus(void) 26 { 27 u32 ret; 28 29 asm volatile("mrs %0, mdccsr_el0" : "=r" (ret)); 30 31 return ret; 32 } 33 34 static inline char __dcc_getchar(void) 35 { 36 char c; 37 38 asm volatile("mrs %0, dbgdtrrx_el0" : "=r" (c)); 39 isb(); 40 41 return c; 42 } 43 44 static inline void __dcc_putchar(char c) 45 { 46 /* 47 * The typecast is to make absolutely certain that 'c' is 48 * zero-extended. 49 */ 50 asm volatile("msr dbgdtrtx_el0, %0" 51 : : "r" ((unsigned long)(unsigned char)c)); 52 isb(); 53 } 54 55 #endif 56