RISC-V: Implement multi-letter ISA extension probing framework

Multi-letter extensions can be probed using exising
riscv_isa_extension_available API now. It doesn't support versioning
right now as there is no use case for it.
Individual extension specific implementation will be added during
each extension support.
Tested-by: NHeiko Stuebner <heiko@sntech.de>
Signed-off-by: NAtish Patra <atishp@rivosinc.com>
Reviewed-by: NAnup Patel <anup@brainfault.org>
Signed-off-by: NPalmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/hwcap.h

@@ -34,7 +34,25 @@ extern unsigned long elf_hwcap;
 #define RISCV_ISA_EXT_s		('s' - 'a')
 #define RISCV_ISA_EXT_u		('u' - 'a')
 
+/*
+ * Increse this to higher value as kernel support more ISA extensions.
+ */
 #define RISCV_ISA_EXT_MAX	64
+#define RISCV_ISA_EXT_NAME_LEN_MAX 32
+
+/* The base ID for multi-letter ISA extensions */
+#define RISCV_ISA_EXT_BASE 26
+
+/*
+ * This enum represent the logical ID for each multi-letter RISC-V ISA extension.
+ * The logical ID should start from RISCV_ISA_EXT_BASE and must not exceed
+ * RISCV_ISA_EXT_MAX. 0-25 range is reserved for single letter
+ * extensions while all the multi-letter extensions should define the next
+ * available logical extension id.
+ */
+enum riscv_isa_ext_id {
+	RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
+};
 
 unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
 

arch/riscv/kernel/cpufeature.c

@@ -83,7 +83,7 @@ void __init riscv_fill_hwcap(void)
 
 	for_each_of_cpu_node(node) {
 		unsigned long this_hwcap = 0;
-		unsigned long this_isa = 0;
+		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
 
 		if (riscv_of_processor_hartid(node) < 0)
 			continue;
@@ -100,6 +100,7 @@ void __init riscv_fill_hwcap(void)
 		if (!strncmp(isa, "rv64", 4))
 			isa += 4;
 #endif
+		bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);
 		for (; *isa; ++isa) {
 			const char *ext = isa++;
 			const char *ext_end = isa;
@@ -172,12 +173,20 @@ void __init riscv_fill_hwcap(void)
 			if (*isa != '_')
 				--isa;
 
+#define SET_ISA_EXT_MAP(name, bit)						\
+			do {							\
+				if ((ext_end - ext == sizeof(name) - 1) &&	\
+				     !memcmp(ext, name, sizeof(name) - 1))	\
+					set_bit(bit, this_isa);			\
+			} while (false)						\
+
 			if (unlikely(ext_err))
 				continue;
 			if (!ext_long) {
 				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
-				this_isa |= (1UL << (*ext - 'a'));
+				set_bit(*ext - 'a', this_isa);
 			}
+#undef SET_ISA_EXT_MAP
 		}
 
 		/*
@@ -190,10 +199,11 @@ void __init riscv_fill_hwcap(void)
 		else
 			elf_hwcap = this_hwcap;
 
-		if (riscv_isa[0])
-			riscv_isa[0] &= this_isa;
+		if (bitmap_weight(riscv_isa, RISCV_ISA_EXT_MAX))
+			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
 		else
-			riscv_isa[0] = this_isa;
+			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+
 	}
 
 	/* We don't support systems with F but without D, so mask those out
@@ -207,7 +217,7 @@ void __init riscv_fill_hwcap(void)
 	for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
 		if (riscv_isa[0] & BIT_MASK(i))
 			print_str[j++] = (char)('a' + i);
-	pr_info("riscv: ISA extensions %s\n", print_str);
+	pr_info("riscv: base ISA extensions %s\n", print_str);
 
 	memset(print_str, 0, sizeof(print_str));
 	for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)