[PATCH v5 4/6] RISC-V: Implement multi-letter ISA extension probing framework

From: Atish Patra
Date: Tue Feb 22 2022 - 15:48:39 EST


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.

Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
---
arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
arch/riscv/kernel/cpufeature.c | 24 ++++++++++++++++++------
2 files changed, 36 insertions(+), 6 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 b0df7eff47f7..c6693873e95c 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;
+ DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);

if (riscv_of_processor_hartid(node) < 0)
continue;
@@ -100,6 +100,7 @@ void __init riscv_fill_hwcap(void)
if (!strncmp(isa, "rv64", 4))
isa += 4;
#endif
+ bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);
for (; *isa; ++isa) {
const char *ext = isa++;
const char *ext_end = isa;
@@ -172,12 +173,22 @@ 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)) { \
+ set_bit(bit, this_isa); \
+ 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'));
+ set_bit(*ext - 'a', this_isa);
}
+#undef SET_ISA_EXT_MAP
}

/*
@@ -190,10 +201,11 @@ void __init riscv_fill_hwcap(void)
else
elf_hwcap = this_hwcap;

- if (riscv_isa[0])
- riscv_isa[0] &= this_isa;
+ if (bitmap_weight(riscv_isa, RISCV_ISA_EXT_MAX))
+ bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
else
- riscv_isa[0] = this_isa;
+ bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
+
}

/* We don't support systems with F but without D, so mask those out
@@ -207,7 +219,7 @@ void __init riscv_fill_hwcap(void)
for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
if (riscv_isa[0] & BIT_MASK(i))
print_str[j++] = (char)('a' + i);
- pr_info("riscv: ISA extensions %s\n", print_str);
+ pr_info("riscv: base ISA extensions %s\n", print_str);

memset(print_str, 0, sizeof(print_str));
for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
--
2.30.2