On Thu, Jun 29, 2023 at 09:28:56AM +0100, Conor Dooley wrote:
> As it says on the tin, provide a Kconfig option to disabling parsing the
> "riscv,isa" devicetree property. Hide the option behind NONPORTABLE so
> that only those willing to keep the pieces enable it, and make sure the
> default kernel contains the fallback code.
>
> Suggested-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> ---
> arch/riscv/Kconfig | 16 ++++++++++++++++
> arch/riscv/kernel/cpu.c | 3 +++
> arch/riscv/kernel/cpufeature.c | 2 +-
> 3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 1d39efe2b940..0e1909ac5947 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -291,6 +291,22 @@ config NONPORTABLE
>
> If unsure, say N.
>
> +config NO_RISCV_ISA_FALLBACK
> + bool "Permit falling back to parsing riscv,isa for extension support"
> + depends on NONPORTABLE
> + help
> + 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 Y here will result in a kernel without this fallback, and
> + will not work on platforms where the devicetree does not contain the
> + replacement properties of "riscv,isa-base" and
^ spacing issue
> + "riscv,isa-extensions". Please see the dt-binding, located at
> + Documentation/devicetree/bindings/riscv/extensions.yaml for details
> + on the replacement properties.
> +
> choice
> prompt "Base ISA"
> default ARCH_RV64I
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 9a4f4a23afcd..86a1d98b8b3b 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -81,6 +81,9 @@ int riscv_early_of_processor_hartid(struct device_node *node, unsigned long *har
> return 0;
>
> old_interface:
> + if (IS_ENABLED(CONFIG_NO_RISCV_ISA_FALLBACK))
> + return -ENODEV;
> +
> if (of_property_read_string(node, "riscv,isa", &isa)) {
> pr_warn("CPU with hartid=%lu has no \"riscv,isa-base\" or \"riscv,isa\" property\n",
> *hart);
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 2c4503fa984f..f6fb18d2af84 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -490,7 +490,7 @@ void __init riscv_fill_hwcap(void)
> } else {
> int ret = riscv_fill_hwcap_from_ext_list(isa2hwcap);
>
> - if (ret) {
> + if (ret && !IS_ENABLED(CONFIG_NO_RISCV_ISA_FALLBACK)) {
> pr_info("Falling back to deprecated \"riscv,isa\"\n");
> riscv_fill_hwcap_from_isa_string(isa2hwcap);
> }
> --
> 2.40.1
>
Should we also have a kernel command line option, 'isa_fallback', where
without this config the command line option is not necessary to fallback,
but, with this config, no fallback will be done unless 'isa_fallback' is
provided?
Thanks,
drew
