arm64: Add macros to read/write system registers

Rather than crafting custom macros for reading/writing each system
register provide generics accessors, read_sysreg and write_sysreg, for
this purpose.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/sysreg.h

@@ -20,6 +20,8 @@
 #ifndef __ASM_SYSREG_H
 #define __ASM_SYSREG_H
 
+#include <linux/stringify.h>
+
 #include <asm/opcodes.h>
 
 /*
@@ -208,6 +210,8 @@
 
 #else
 
+#include <linux/types.h>
+
 asm(
 "	.irp	num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30\n"
 "	.equ	__reg_num_x\\num, \\num\n"
@@ -232,6 +236,23 @@ static inline void config_sctlr_el1(u32 clear, u32 set)
 	val |= set;
 	asm volatile("msr sctlr_el1, %0" : : "r" (val));
 }
+
+/*
+ * Unlike read_cpuid, calls to read_sysreg are never expected to be
+ * optimized away or replaced with synthetic values.
+ */
+#define read_sysreg(r) ({					\
+	u64 __val;						\
+	asm volatile("mrs %0, " __stringify(r) : "=r" (__val));	\
+	__val;							\
+})
+
+#define write_sysreg(v, r) do {					\
+	u64 __val = (u64)v;					\
+	asm volatile("msr " __stringify(r) ", %0"		\
+		     : : "r" (__val));				\
+} while (0)
+
 #endif
 
 #endif	/* __ASM_SYSREG_H */