CONFIG_RISCV_ISA_FALLBACK is not available for thedefaultarchitecture x86.
Result is shown for architecture riscv
Permit falling back to parsing riscv,isa for extension support by default
configname: CONFIG_RISCV_ISA_FALLBACK
Linux Kernel Configuration
└─>Boot options
└─>Permit falling back to parsing riscv,isa for extension support by default
In linux kernel since version 4.14.327 (release Date: 2023-10-10)
Parsing the "riscv,isa" devicetree property has been deprecated and
replaced by a list of explicitly defined strings. For compatibility
with existing platforms, the kernel will fall back to parsing the
"riscv,isa" property if the replacements are not found.
Selecting N here will result in a kernel that does not use the
fallback, unless the commandline "riscv_isa_fallback" parameter is
present.
Please see the dt-binding, located at
Documentation/devicetree/bindings/riscv/extensions.yaml for details
on the replacement properties, "riscv,isa-base" and
"riscv,isa-extensions".
replaced by a list of explicitly defined strings. For compatibility
with existing platforms, the kernel will fall back to parsing the
"riscv,isa" property if the replacements are not found.
Selecting N here will result in a kernel that does not use the
fallback, unless the commandline "riscv_isa_fallback" parameter is
present.
Please see the dt-binding, located at
Documentation/devicetree/bindings/riscv/extensions.yaml for details
on the replacement properties, "riscv,isa-base" and
"riscv,isa-extensions".