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Subject[PATCH 2/4] RISC-V: Add riscv_isa reprensenting ISA features common across CPUs
Date
From: Anup Patel <anup.patel@wdc.com>

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@wdc.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
arch/riscv/include/asm/hwcap.h | 25 ++++++++++++++++++++++
arch/riscv/kernel/cpufeature.c | 39 +++++++++++++++++++++++++++++++---
2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 7ecb7c6a57b1..e069f60ad5d2 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -22,5 +22,30 @@ enum {
};

extern unsigned long elf_hwcap;
+
+#define RISCV_ISA_EXT_A (1UL << ('A' - 'A'))
+#define RISCV_ISA_EXT_a RISCV_ISA_EXT_A
+#define RISCV_ISA_EXT_C (1UL << ('C' - 'A'))
+#define RISCV_ISA_EXT_c RISCV_ISA_EXT_C
+#define RISCV_ISA_EXT_D (1UL << ('D' - 'A'))
+#define RISCV_ISA_EXT_d RISCV_ISA_EXT_D
+#define RISCV_ISA_EXT_F (1UL << ('F' - 'A'))
+#define RISCV_ISA_EXT_f RISCV_ISA_EXT_F
+#define RISCV_ISA_EXT_H (1UL << ('H' - 'A'))
+#define RISCV_ISA_EXT_h RISCV_ISA_EXT_H
+#define RISCV_ISA_EXT_I (1UL << ('I' - 'A'))
+#define RISCV_ISA_EXT_i RISCV_ISA_EXT_I
+#define RISCV_ISA_EXT_M (1UL << ('M' - 'A'))
+#define RISCV_ISA_EXT_m RISCV_ISA_EXT_M
+#define RISCV_ISA_EXT_S (1UL << ('S' - 'A'))
+#define RISCV_ISA_EXT_s RISCV_ISA_EXT_S
+#define RISCV_ISA_EXT_U (1UL << ('U' - 'A'))
+#define RISCV_ISA_EXT_u RISCV_ISA_EXT_U
+
+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..d76c806b4fc9 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -12,6 +12,7 @@
#include <asm/smp.h>

unsigned long elf_hwcap __read_mostly;
+unsigned long riscv_isa __read_mostly;
#ifdef CONFIG_FPU
bool has_fpu __read_mostly;
#endif
@@ -20,7 +21,8 @@ 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 +33,11 @@ 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 +47,22 @@ void riscv_fill_hwcap(void)
continue;
}

- for (i = 0; i < strlen(isa); ++i)
+ i = 0;
+ isa_len = strlen(isa);
+#if defined(CONFIG_32BIT)
+ if (strncasecmp(isa, "rv32", 4) != 0)
+ i += 4;
+#elif defined(CONFIG_64BIT)
+ if (strncasecmp(isa, "rv64", 4) != 0)
+ 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'));
+ 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
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