[PATCH v3 1/3] RISC-V: Improve use of isa2hwcap[]

Andrew Jones
2022-11-29T14:35:13Z

Improve isa2hwcap[] by removing it from static storage, as
riscv_fill_hwcap() is only called once, and by reducing its size
from 256 bytes to 26. The latter improvement is possible because
isa2hwcap[] will never be indexed with capital letters and we can
precompute the offsets from 'a'.

No functional change intended.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
---
arch/riscv/kernel/cpufeature.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 694267d1fe81..4677320d7e31 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -74,15 +74,15 @@ void __init riscv_fill_hwcap(void)
const char *isa;
char print_str[NUM_ALPHA_EXTS + 1];
int i, j, rc;
- static unsigned long isa2hwcap[256] = {0};
+ unsigned long isa2hwcap[26] = {0};
unsigned long hartid;

- isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
- isa2hwcap['m'] = isa2hwcap['M'] = COMPAT_HWCAP_ISA_M;
- isa2hwcap['a'] = isa2hwcap['A'] = COMPAT_HWCAP_ISA_A;
- isa2hwcap['f'] = isa2hwcap['F'] = COMPAT_HWCAP_ISA_F;
- isa2hwcap['d'] = isa2hwcap['D'] = COMPAT_HWCAP_ISA_D;
- isa2hwcap['c'] = isa2hwcap['C'] = COMPAT_HWCAP_ISA_C;
+ isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
+ isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
+ isa2hwcap['a' - 'a'] = COMPAT_HWCAP_ISA_A;
+ isa2hwcap['f' - 'a'] = COMPAT_HWCAP_ISA_F;
+ isa2hwcap['d' - 'a'] = COMPAT_HWCAP_ISA_D;
+ isa2hwcap['c' - 'a'] = COMPAT_HWCAP_ISA_C;

elf_hwcap = 0;

@@ -196,8 +196,10 @@ void __init riscv_fill_hwcap(void)
if (unlikely(ext_err))
continue;
if (!ext_long) {
- this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
- set_bit(*ext - 'a', this_isa);
+ int nr = *ext - 'a';
+
+ this_hwcap |= isa2hwcap[nr];
+ set_bit(nr, this_isa);
} else {
SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
--
2.38.1