[PATCH] arm64: runtime-const: save one instruction when ARM64_VA_BITS <= 48

[Jisheng Zhang]

Currently, the runtime_const_ptr() uses 4 instructions to move a long
imm to GP, but when ARM64_VA_BITS <= 48(which is true for android and
armbian), the top 8bits of runtime cont ptr is all '1', so we can make
use of the movn instruction to construct the imm's top 8bits and lower
16bits at the same time, thus save one instruction.

Signed-off-by: Jisheng Zhang <jszhang at kernel.org>
---
 arch/arm64/include/asm/runtime-const.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/arm64/include/asm/runtime-const.h b/arch/arm64/include/asm/runtime-const.h
index be5915669d23..6797dd37d690 100644
--- a/arch/arm64/include/asm/runtime-const.h
+++ b/arch/arm64/include/asm/runtime-const.h
@@ -7,6 +7,8 @@
 /* Sigh. You can still run arm64 in BE mode */
 #include <asm/byteorder.h>
 
+#if CONFIG_ARM64_VA_BITS > 48
+
 #define runtime_const_ptr(sym) ({				\
 	typeof(sym) __ret;					\
 	asm_inline("1:\t"					\
@@ -20,6 +22,22 @@
 		:"=r" (__ret));					\
 	__ret; })
 
+#else
+
+#define runtime_const_ptr(sym) ({				\
+	typeof(sym) __ret;					\
+	asm_inline("1:\t"					\
+		"movn %0, #0x3210\n\t"				\
+		"movk %0, #0x89ab, lsl #16\n\t"			\
+		"movk %0, #0x4567, lsl #32\n\t"			\
+		".pushsection runtime_ptr_" #sym ",\"a\"\n\t"	\
+		".long 1b - .\n\t"				\
+		".popsection"					\
+		: "=r" (__ret));				\
+	__ret; })
+
+#endif
+
 #define runtime_const_shift_right_32(val, sym) ({		\
 	unsigned long __ret;					\
 	asm_inline("1:\t"					\
@@ -58,11 +76,19 @@ static inline void __runtime_fixup_caches(void *where, unsigned int insns)
 static inline void __runtime_fixup_ptr(void *where, unsigned long val)
 {
 	__le32 *p = lm_alias(where);
+#if CONFIG_ARM64_VA_BITS > 48
 	__runtime_fixup_16(p, val);
+#else
+	__runtime_fixup_16(p, ~val);
+#endif
 	__runtime_fixup_16(p+1, val >> 16);
 	__runtime_fixup_16(p+2, val >> 32);
+#if CONFIG_ARM64_VA_BITS > 48
 	__runtime_fixup_16(p+3, val >> 48);
 	__runtime_fixup_caches(where, 4);
+#else
+	__runtime_fixup_caches(where, 3);
+#endif
 }
 
 /* Immediate value is 6 bits starting at bit #16 */
-- 
2.51.0