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Subject[PATCH v1 1/2] RISC-V: add non-alternative fallback for riscv_has_extension_[un]likely()
Date
The has_fpu() check, which in turn calls riscv_has_extension_likely(),
relies on alternatives to figure out whether the system has an FPU.
As a result, it will malfunction on XIP kernels, as they do not support
the alternatives mechanism.

When alternatives support is not present, fall back to using
__riscv_isa_extension_available() in riscv_has_extension_[un]likely()
instead stead, which handily takes the same argument, so that kernels
that do not support alternatives can accurately report the presence of
FPU support.

Fixes: 702e64550b12 ("riscv: fpu: switch has_fpu() to riscv_has_extension_likely()")
Link: https://lore.kernel.org/all/ad445951-3d13-4644-94d9-e0989cda39c3@spud/
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
arch/riscv/include/asm/hwcap.h | 50 ++++++++++++++++++++--------------
1 file changed, 30 insertions(+), 20 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index e3021b2590de..6263a0de1c6a 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -57,18 +57,31 @@ struct riscv_isa_ext_data {
unsigned int isa_ext_id;
};

+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)
+
static __always_inline bool
riscv_has_extension_likely(const unsigned long ext)
{
compiletime_assert(ext < RISCV_ISA_EXT_MAX,
"ext must be < RISCV_ISA_EXT_MAX");

- asm_volatile_goto(
- ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
- :
- : [ext] "i" (ext)
- :
- : l_no);
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
+ :
+ : [ext] "i" (ext)
+ :
+ : l_no);
+ } else {
+ if (!__riscv_isa_extension_available(NULL, ext))
+ goto l_no;
+ }

return true;
l_no:
@@ -81,26 +94,23 @@ riscv_has_extension_unlikely(const unsigned long ext)
compiletime_assert(ext < RISCV_ISA_EXT_MAX,
"ext must be < RISCV_ISA_EXT_MAX");

- asm_volatile_goto(
- ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
- :
- : [ext] "i" (ext)
- :
- : l_yes);
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+ asm_volatile_goto(
+ ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
+ :
+ : [ext] "i" (ext)
+ :
+ : l_yes);
+ } else {
+ if (__riscv_isa_extension_available(NULL, ext))
+ goto l_yes;
+ }

return false;
l_yes:
return true;
}

-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 /* _ASM_RISCV_HWCAP_H */
--
2.39.2
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