arm64: sysreg: replace open-coded mrs_s/msr_s with {read,write}_sysreg_s

Similar to our {read,write}_sysreg accessors for architected, named
system registers, this patch introduces {read,write}_sysreg_s variants
that can take arbitrary sys_reg output and therefore access IMPDEF
registers or registers that unsupported by binutils.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/cputype.h

@@ -93,11 +93,7 @@
 
 #include <asm/sysreg.h>
 
-#define read_cpuid(reg) ({						\
-	u64 __val;							\
-	asm("mrs_s	%0, " __stringify(SYS_ ## reg) : "=r" (__val));	\
-	__val;								\
-})
+#define read_cpuid(reg)			read_sysreg_s(SYS_ ## reg)
 
 /*
  * The CPU ID never changes at run time, so we might as well tell the

arch/arm64/include/asm/sysreg.h

@@ -274,6 +274,21 @@ asm(
 		     : : "rZ" (__val));				\
 } while (0)
 
+/*
+ * For registers without architectural names, or simply unsupported by
+ * GAS.
+ */
+#define read_sysreg_s(r) ({						\
+	u64 __val;							\
+	asm volatile("mrs_s %0, " __stringify(r) : "=r" (__val));	\
+	__val;								\
+})
+
+#define write_sysreg_s(v, r) do {					\
+	u64 __val = (u64)v;						\
+	asm volatile("msr_s " __stringify(r) ", %0" : : "rZ" (__val));	\
+} while (0)
+
 static inline void config_sctlr_el1(u32 clear, u32 set)
 {
 	u32 val;