ARM64: TTY: hvc_dcc: Add support for ARM64 dcc

/* Copyright (c) 2014-2015 The Linux Foundation. All rights reserved.

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 and

 * only version 2 as published by the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * A call to __dcc_getchar() or __dcc_putchar() is typically followed by

 * a call to __dcc_getstatus().  We want to make sure that the CPU does

 * not speculative read the DCC status before executing the read or write

 * instruction.  That's what the ISBs are for.

 *

 * The 'volatile' ensures that the compiler does not cache the status bits,

 * and instead reads the DCC register every time.

 */

#ifndef __ASM_DCC_H

#define __ASM_DCC_H

#include <asm/barrier.h>

static inline u32 __dcc_getstatus(void)

{

	u32 ret;

	asm volatile("mrs %0, mdccsr_el0" : "=r" (ret));

	return ret;

}

static inline char __dcc_getchar(void)

{

	char c;

	asm volatile("mrs %0, dbgdtrrx_el0" : "=r" (c));

	isb();

	return c;

}

static inline void __dcc_putchar(char c)

{

	/*

	 * The typecast is to make absolutely certain that 'c' is

	 * zero-extended.

	 */

	asm volatile("msr dbgdtrtx_el0, %0"

			: : "r" ((unsigned long)(unsigned char)c));

	isb();

}

#endif

config HVC_DCC

       bool "ARM JTAG DCC console"

       depends on ARM

       depends on ARM || ARM64

       select HVC_DRIVER

       help

         This console uses the JTAG DCC on ARM to create a console under the HVC