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Subject[PATCH v6 02/21] RISC-V: Add bitmap reprensenting ISA features common across CPUs
Date
This patch adds riscv_isa bitmap which represents Host ISA features
common across all Host 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 for riscv_isa bitmap is in KVM hypervisor where
we will use it 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>
Reviewed-by: Alexander Graf <graf@amazon.com>
---
arch/riscv/include/asm/hwcap.h | 26 +++++++++++
arch/riscv/kernel/cpufeature.c | 79 ++++++++++++++++++++++++++++++++--
2 files changed, 102 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 7ecb7c6a57b1..9b657375aa51 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -8,6 +8,7 @@
#ifndef __ASM_HWCAP_H
#define __ASM_HWCAP_H

+#include <linux/bits.h>
#include <uapi/asm/hwcap.h>

#ifndef __ASSEMBLY__
@@ -22,5 +23,30 @@ enum {
};

extern unsigned long elf_hwcap;
+
+#define RISCV_ISA_EXT_a ('a' - 'a')
+#define RISCV_ISA_EXT_c ('c' - 'a')
+#define RISCV_ISA_EXT_d ('d' - 'a')
+#define RISCV_ISA_EXT_f ('f' - 'a')
+#define RISCV_ISA_EXT_h ('h' - 'a')
+#define RISCV_ISA_EXT_i ('i' - 'a')
+#define RISCV_ISA_EXT_m ('m' - 'a')
+#define RISCV_ISA_EXT_s ('s' - 'a')
+#define RISCV_ISA_EXT_u ('u' - 'a')
+#define RISCV_ISA_EXT_zicsr (('z' - 'a') + 1)
+#define RISCV_ISA_EXT_zifencei (('z' - 'a') + 2)
+#define RISCV_ISA_EXT_zam (('z' - 'a') + 3)
+#define RISCV_ISA_EXT_ztso (('z' - 'a') + 4)
+
+#define RISCV_ISA_EXT_MAX 256
+
+unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
+
+#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
+
+bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
+#define riscv_isa_extension_available(isa_bitmap, ext) \
+ __riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
+
#endif
#endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index b1ade9a49347..4ce71ce5e290 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -6,21 +6,64 @@
* Copyright (C) 2017 SiFive
*/

+#include <linux/bitmap.h>
#include <linux/of.h>
#include <asm/processor.h>
#include <asm/hwcap.h>
#include <asm/smp.h>

unsigned long elf_hwcap __read_mostly;
+
+/* Host ISA bitmap */
+static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
+
#ifdef CONFIG_FPU
bool has_fpu __read_mostly;
#endif

+/**
+ * riscv_isa_extension_base - Get base extension word
+ *
+ * @isa_bitmap ISA bitmap to use
+ * @returns base extension word as unsigned long value
+ *
+ * NOTE: If isa_bitmap is NULL then Host ISA bitmap will be used.
+ */
+unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap)
+{
+ if (!isa_bitmap)
+ return riscv_isa[0];
+ return isa_bitmap[0];
+}
+EXPORT_SYMBOL_GPL(riscv_isa_extension_base);
+
+/**
+ * __riscv_isa_extension_available - Check whether given extension
+ * is available or not
+ *
+ * @isa_bitmap ISA bitmap to use
+ * @bit bit position of the desired extension
+ * @returns true or false
+ *
+ * NOTE: If isa_bitmap is NULL then Host ISA bitmap will be used.
+ */
+bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit)
+{
+ const unsigned long *bmap = (isa_bitmap) ? isa_bitmap : riscv_isa;
+
+ if (bit >= RISCV_ISA_EXT_MAX)
+ return false;
+
+ return test_bit(bit, bmap) ? true : false;
+}
+EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
+
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;
@@ -32,8 +75,11 @@ void riscv_fill_hwcap(void)

elf_hwcap = 0;

+ bitmap_zero(riscv_isa, RISCV_ISA_EXT_MAX);
+
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 +89,20 @@ 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 +113,11 @@ void riscv_fill_hwcap(void)
elf_hwcap &= this_hwcap;
else
elf_hwcap = this_hwcap;
+
+ if (riscv_isa[0])
+ riscv_isa[0] &= this_isa;
+ else
+ riscv_isa[0] = this_isa;
}

/* We don't support systems with F but without D, so mask those out
@@ -64,7 +127,17 @@ 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[0] & BIT_MASK(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 & BIT_MASK(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))
--
2.17.1
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