riscv: Add macro for multiple nop instructions

Some cases need multiple nop instructions and arm64 already has a
nice helper for not needing to write all of them out but instead
use a helper to add n nops.

So add a similar thing to riscv and convert the T-Head PMA
alternative to use it.

* 'riscv-nops' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git:
  riscv: convert the t-head pbmt errata to use the __nops macro
  riscv: introduce nops and __nops macros for NOP sequences

Author: palmer-dabbelt

arch/riscv/include/asm/asm.h

@@ -67,4 +67,19 @@
 #error "Unexpected __SIZEOF_SHORT__"
 #endif
 
+#ifdef __ASSEMBLY__
+
+/* Common assembly source macros */
+
+/*
+ * NOP sequence
+ */
+.macro	nops, num
+	.rept	\num
+	nop
+	.endr
+.endm
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ASM_RISCV_ASM_H */

arch/riscv/include/asm/barrier.h

@@ -13,6 +13,8 @@
 #ifndef __ASSEMBLY__
 
 #define nop()		__asm__ __volatile__ ("nop")
+#define __nops(n)	".rept	" #n "\nnop\n.endr\n"
+#define nops(n)		__asm__ __volatile__ (__nops(n))
 
 #define RISCV_FENCE(p, s) \
 	__asm__ __volatile__ ("fence " #p "," #s : : : "memory")

arch/riscv/include/asm/errata_list.h

@@ -68,13 +68,7 @@ asm(ALTERNATIVE_2("li %0, 0\t\nnop",					\
  */
 #define ALT_THEAD_PMA(_val)						\
 asm volatile(ALTERNATIVE(						\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop",								\
+	__nops(7),							\
 	"li      t3, %2\n\t"						\
 	"slli    t3, t3, %4\n\t"					\
 	"and     t3, %0, t3\n\t"					\