1 files changed, 41 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h
new file mode 100644
index 000000000..ebd9fb472
--- /dev/null
+++ b/arch/arm64/include/asm/dcc.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2014-2015 The Linux Foundation. All rights reserved.
+ *
+ * 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>
+#include <asm/sysreg.h>
+
+static inline u32 __dcc_getstatus(void)
+{
+	return read_sysreg(mdccsr_el0);
+}
+
+static inline char __dcc_getchar(void)
+{
+	char c = read_sysreg(dbgdtrrx_el0);
+	isb();
+
+	return c;
+}
+
+static inline void __dcc_putchar(char c)
+{
+	/*
+	 * The typecast is to make absolutely certain that 'c' is
+	 * zero-extended.
+	 */
+	write_sysreg((unsigned char)c, dbgdtrtx_el0);
+	isb();
+}
+
+#endif