[PATCH v2 4/6] RISC-V: Implement multi-letter ISA extension probing framework

[Atish Patra <atishp@rivosinc.com>]

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.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
 arch/riscv/kernel/cpufeature.c | 27 ++++++++++++++++++++++++---
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 5ce50468aff1..170bd80da520 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/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);
 
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index e9e3b0693d16..469b9739faf7 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/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;
+		uint64_t this_isa = 0;
 
 		if (riscv_of_processor_hartid(node) < 0)
 			continue;
@@ -169,12 +169,22 @@ 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)) {    \
+					this_isa |= (1UL << bit);		\
+					pr_info("Found ISA extension %s", name);\
+				}						\
+			} while (false)						\
+
 			if (unlikely(ext_err))
 				continue;
 			if (!ext_long) {
 				this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
 				this_isa |= (1UL << (*ext - 'a'));
 			}
+#undef SET_ISA_EXT_MAP
 		}
 
 		/*
@@ -187,10 +197,21 @@ void __init riscv_fill_hwcap(void)
 		else
 			elf_hwcap = this_hwcap;
 
-		if (riscv_isa[0])
+		if (riscv_isa[0]) {
+#if IS_ENABLED(CONFIG_32BIT)
+			riscv_isa[0] &= this_isa & 0xFFFFFFFF;
+			riscv_isa[1] &= this_isa >> 32;
+#else
 			riscv_isa[0] &= this_isa;
-		else
+#endif
+		} else {
+#if IS_ENABLED(CONFIG_32BIT)
+			riscv_isa[0] = this_isa & 0xFFFFFFFF;
+			riscv_isa[1] = this_isa >> 32;
+#else
 			riscv_isa[0] = this_isa;
+#endif
+		}
 	}
 
 	/* We don't support systems with F but without D, so mask those out
-- 
2.30.2