[PATCH v4 2/4] RISC-V: Add riscv_isa reprensenting ISA features common across CPUs

[Atish Patra]

From: Anup Patel <anup.patel@xxxxxxx>

This patch adds riscv_isa integer to represent ISA features common
across all CPUs. The riscv_isa is not same as elf_hwcap because
elf_hwcap will only have ISA features relevant for user-space apps
whereas riscv_isa will have ISA features relevant to both kernel
and user-space apps.

One of the use case is KVM hypervisor where riscv_isa will be used
to do following operations:

1. Check whether hypervisor extension is available
2. Find ISA features that need to be virtualized (e.g. floating
   point support, vector extension, etc.)

Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
---
 arch/riscv/include/asm/hwcap.h | 16 ++++++++++++++
 arch/riscv/kernel/cpufeature.c | 39 +++++++++++++++++++++++++++++++---
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 7ecb7c6a57b1..717306780add 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -22,5 +22,21 @@ enum {
 };
 
 extern unsigned long elf_hwcap;
+
+#define RISCV_ISA_EXT_a		(1UL << ('a' - 'a'))
+#define RISCV_ISA_EXT_c		(1UL << ('c' - 'a'))
+#define RISCV_ISA_EXT_d		(1UL << ('d' - 'a'))
+#define RISCV_ISA_EXT_f		(1UL << ('f' - 'a'))
+#define RISCV_ISA_EXT_h		(1UL << ('h' - 'a'))
+#define RISCV_ISA_EXT_i		(1UL << ('i' - 'a'))
+#define RISCV_ISA_EXT_m		(1UL << ('m' - 'a'))
+#define RISCV_ISA_EXT_s		(1UL << ('s' - 'a'))
+#define RISCV_ISA_EXT_u		(1UL << ('u' - 'a'))
+
+extern unsigned long riscv_isa;
+
+#define riscv_isa_extension_available(ext_char)	\
+		(riscv_isa & RISCV_ISA_EXT_##ext_char)
+
 #endif
 #endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index b1ade9a49347..becc99272341 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -12,6 +12,9 @@
 #include <asm/smp.h>
 
 unsigned long elf_hwcap __read_mostly;
+unsigned long riscv_isa __read_mostly;
+EXPORT_SYMBOL_GPL(riscv_isa);
+
 #ifdef CONFIG_FPU
 bool has_fpu __read_mostly;
 #endif
@@ -20,7 +23,8 @@ void riscv_fill_hwcap(void)
 {
 	struct device_node *node;
 	const char *isa;
-	size_t i;
+	char print_str[BITS_PER_LONG+1];
+	size_t i, j, isa_len;
 	static unsigned long isa2hwcap[256] = {0};
 
 	isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
@@ -31,9 +35,11 @@ void riscv_fill_hwcap(void)
 	isa2hwcap['c'] = isa2hwcap['C'] = COMPAT_HWCAP_ISA_C;
 
 	elf_hwcap = 0;
+	riscv_isa = 0;
 
 	for_each_of_cpu_node(node) {
 		unsigned long this_hwcap = 0;
+		unsigned long this_isa = 0;
 
 		if (riscv_of_processor_hartid(node) < 0)
 			continue;
@@ -43,8 +49,20 @@ void riscv_fill_hwcap(void)
 			continue;
 		}
 
-		for (i = 0; i < strlen(isa); ++i)
+		i = 0;
+		isa_len = strlen(isa);
+#if defined(CONFIG_32BIT)
+		if (!strncmp(isa, "rv32", 4))
+			i += 4;
+#elif defined(CONFIG_64BIT)
+		if (!strncmp(isa, "rv64", 4))
+			i += 4;
+#endif
+		for (; i < isa_len; ++i) {
 			this_hwcap |= isa2hwcap[(unsigned char)(isa[i])];
+			if ('a' <= isa[i] && isa[i] <= 'z')
+				this_isa |= (1UL << (isa[i] - 'a'));
+		}
 
 		/*
 		 * All "okay" hart should have same isa. Set HWCAP based on
@@ -55,6 +73,11 @@ void riscv_fill_hwcap(void)
 			elf_hwcap &= this_hwcap;
 		else
 			elf_hwcap = this_hwcap;
+
+		if (riscv_isa)
+			riscv_isa &= this_isa;
+		else
+			riscv_isa = this_isa;
 	}
 
 	/* We don't support systems with F but without D, so mask those out
@@ -64,7 +87,17 @@ void riscv_fill_hwcap(void)
 		elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
 	}
 
-	pr_info("elf_hwcap is 0x%lx\n", elf_hwcap);
+	memset(print_str, 0, sizeof(print_str));
+	for (i = 0, j = 0; i < BITS_PER_LONG; i++)
+		if (riscv_isa & (1UL << i))
+			print_str[j++] = (char)('a' + i);
+	pr_info("riscv: ISA extensions %s\n", print_str);
+
+	memset(print_str, 0, sizeof(print_str));
+	for (i = 0, j = 0; i < BITS_PER_LONG; i++)
+		if (elf_hwcap & (1UL << i))
+			print_str[j++] = (char)('a' + i);
+	pr_info("riscv: ELF capabilities %s\n", print_str);
 
 #ifdef CONFIG_FPU
 	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
-- 
2.21.0