MIPS: XPA: Use XPA instructions in assembly

Utilise XPA instructions MFHC0 & MTHC0 in inline assembly instead of
directly encoding them with the _ASM_INSN* macros, and transparently
implement these instructions as assembler macros if the toolchain
doesn't support them natively, using the recently introduced assembler
macro helpers.

The old direct encodings were restricted to using the register $at, so
this allows the extra register moves to go away (saving a grand total of
24 bytes).

Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17775/

arch/mips/Makefile

@@ -216,6 +216,12 @@ cflags-$(toolchain-msa)			+= -DTOOLCHAIN_SUPPORTS_MSA
 endif
 toolchain-virt				:= $(call cc-option-yn,$(mips-cflags) -mvirt)
 cflags-$(toolchain-virt)		+= -DTOOLCHAIN_SUPPORTS_VIRT
+# For -mmicromips, use -Wa,-fatal-warnings to catch unsupported -mxpa which
+# only warns
+xpa-cflags-y				:= $(mips-cflags)
+xpa-cflags-$(micromips-ase)		+= -mmicromips -Wa$(comma)-fatal-warnings
+toolchain-xpa				:= $(call cc-option-yn,$(xpa-cflags-y) -mxpa)
+cflags-$(toolchain-xpa)			+= -DTOOLCHAIN_SUPPORTS_XPA
 
 #
 # Firmware support

arch/mips/include/asm/mipsregs.h

@@ -1504,18 +1504,27 @@ do {									\
 	local_irq_restore(__flags);					\
 } while (0)
 
+#ifndef TOOLCHAIN_SUPPORTS_XPA
+_ASM_MACRO_2R_1S(mfhc0, rt, rs, sel,
+	_ASM_INSN_IF_MIPS(0x40400000 | __rt << 16 | __rs << 11 | \\sel)
+	_ASM_INSN32_IF_MM(0x000000f4 | __rt << 21 | __rs << 16 | \\sel << 11));
+_ASM_MACRO_2R_1S(mthc0, rt, rd, sel,
+	_ASM_INSN_IF_MIPS(0x40c00000 | __rt << 16 | __rd << 11 | \\sel)
+	_ASM_INSN32_IF_MM(0x000002f4 | __rt << 21 | __rd << 16 | \\sel << 11));
+#define _ASM_SET_XPA ""
+#else	/* !TOOLCHAIN_SUPPORTS_XPA */
+#define _ASM_SET_XPA ".set\txpa\n\t"
+#endif
+
 #define __readx_32bit_c0_register(source)				\
 ({									\
 	unsigned int __res;						\
 									\
 	__asm__ __volatile__(						\
 	"	.set	push					\n"	\
-	"	.set	noat					\n"	\
 	"	.set	mips32r2				\n"	\
-	"	# mfhc0 $1, %1					\n"	\
-	_ASM_INSN_IF_MIPS(0x40410000 | ((%1 & 0x1f) << 11))		\
-	_ASM_INSN32_IF_MM(0x002000f4 | ((%1 & 0x1f) << 16))		\
-	"	move	%0, $1					\n"	\
+	_ASM_SET_XPA							\
+	"	mfhc0	%0, $%1					\n"	\
 	"	.set	pop					\n"	\
 	: "=r" (__res)							\
 	: "i" (source));						\
@@ -1526,12 +1535,9 @@ do {									\
 do {									\
 	__asm__ __volatile__(						\
 	"	.set	push					\n"	\
-	"	.set	noat					\n"	\
 	"	.set	mips32r2				\n"	\
-	"	move	$1, %0					\n"	\
-	"	# mthc0 $1, %1					\n"	\
-	_ASM_INSN_IF_MIPS(0x40c10000 | ((%1 & 0x1f) << 11))		\
-	_ASM_INSN32_IF_MM(0x002002f4 | ((%1 & 0x1f) << 16))		\
+	_ASM_SET_XPA							\
+	"	mthc0	%0, $%1					\n"	\
 	"	.set	pop					\n"	\
 	:								\
 	: "r" (value), "i" (register));					\