Re: [PATCH v1 8/9] RISC-V: enable extension detection from new properties

Andrew Jones
2023-06-26T16:24:20Z

On Mon, Jun 26, 2023 at 12:19:46PM +0100, Conor Dooley wrote:
> Add support for parsing the new riscv,isa-extensions property in
> riscv_fill_hwcap(), by means of a new "property" member of the
> riscv_isa_ext_data struct. For now, this shadows the name of the
> extension, however this may not be the case for all extensions.
> For the sake of backwards compatibility, fall back to the old scheme
> if the new properties are not detected. For now, just inform, rather
> than warn, when that happens.
>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
> Naming things is hard, didn't know what to call the new function...

riscv_fill_hwcap_from_isa_extensions() ?

_new() won't age well.

> ---
> arch/riscv/include/asm/hwcap.h | 1 +
> arch/riscv/kernel/cpufeature.c | 80 ++++++++++++++++++++++++++++++----
> 2 files changed, 72 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 6ad896dc4342..e7f235868aa2 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -77,6 +77,7 @@ unsigned long riscv_get_elf_hwcap(void);
> struct riscv_isa_ext_data {
> const unsigned int id;
> const char *name;
> + const char *property;
> const bool multi_letter;
> };
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 366477ba1eea..72eb757ad871 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -101,6 +101,7 @@ static bool riscv_isa_extension_check(int id)
>
> #define __RISCV_ISA_EXT_DATA(_name, _id, _multi) { \
> .name = #_name, \
> + .property = #_name, \
> .id = _id, \
> .multi_letter = _multi, \
> }
> @@ -416,16 +417,66 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
> acpi_put_table((struct acpi_table_header *)rhct);
> }
>
> +static int __init riscv_fill_hwcap_new(unsigned long *isa2hwcap)
> +{
> + unsigned int cpu;
> +
> + for_each_possible_cpu(cpu) {
> + unsigned long this_hwcap = 0;
> + struct device_node *cpu_node;
> + DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
> +
> + cpu_node = of_cpu_device_node_get(cpu);
> + if (!cpu_node) {
> + pr_warn("Unable to find cpu node\n");
> + continue;
> + }
> +
> + if (!of_property_present(cpu_node, "riscv,isa-extensions"))
> + continue;
> +
> + for (int i = 0; i < riscv_isa_ext_count; i++) {
> + if (of_property_match_string(cpu_node, "riscv,isa-extensions",
> + riscv_isa_ext[i].name) < 0)
> + continue;
> +
> + if (!riscv_isa_extension_check(riscv_isa_ext[i].id))
> + continue;
> +
> + if (!riscv_isa_ext[i].multi_letter)
> + this_hwcap |= isa2hwcap[riscv_isa_ext[i].id];
> +
> + set_bit(riscv_isa_ext[i].id, this_isa);
> + }
> +
> + of_node_put(cpu_node);
> +
> + /*
> + * All "okay" harts should have same isa. Set HWCAP based on
> + * common capabilities of every "okay" hart, in case they don't.
> + */
> + if (elf_hwcap)
> + elf_hwcap &= this_hwcap;
> + else
> + elf_hwcap = this_hwcap;
> +
> + if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
> + bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> + else
> + bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> + }
> +
> + if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
> + return -ENOENT;
> +
> + return 0;
> +}
> +
> void __init riscv_fill_hwcap(void)
> {
> - struct device_node *node;
> - const char *isa;
> char print_str[NUM_ALPHA_EXTS + 1];
> - int i, j, rc;
> unsigned long isa2hwcap[26] = {0};
> - struct acpi_table_header *rhct;
> - acpi_status status;
> - unsigned int cpu;
> + int i, j;
>
> isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
> isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
> @@ -435,10 +486,21 @@ void __init riscv_fill_hwcap(void)
> isa2hwcap['c' - 'a'] = COMPAT_HWCAP_ISA_C;
> isa2hwcap['v' - 'a'] = COMPAT_HWCAP_ISA_V;
>
> - riscv_fill_hwcap_from_isa_string(isa2hwcap);
> + if (!acpi_disabled) {
> + riscv_fill_hwcap_from_isa_string(isa2hwcap);
> + } else {
> + int ret = riscv_fill_hwcap_new(isa2hwcap);
>
> - /* We don't support systems with F but without D, so mask those out
> - * here. */
> + if (ret) {
> + pr_info("Falling back to deprecated \"riscv,isa\"\n");
> + riscv_fill_hwcap_from_isa_string(isa2hwcap);
> + }
> + }
> +
> + /*
> + * We don't support systems with F but without D, so mask those out
> + * here.
> + */
> if ((elf_hwcap & COMPAT_HWCAP_ISA_F) && !(elf_hwcap & COMPAT_HWCAP_ISA_D)) {
> pr_info("This kernel does not support systems with F but not D\n");
> elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
> --
> 2.40.1
>

Other than the name and moving the removal of the unused declarations to
the previous patch,

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks,
drew