Re: [PATCH v4 06/16] riscv: Introduce vendor variants of extension helpers

Conor Dooley
2024-05-01T11:30:03Z

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On Fri, Apr 26, 2024 at 02:29:20PM -0700, Charlie Jenkins wrote:

> index c073494519eb..dd7e8e0c0af1 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -844,25 +844,41 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
> {
> struct alt_entry *alt;
> void *oldptr, *altptr;
> - u16 id, value;
> + u16 id, value, vendor;
>
> if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> return;
>
> for (alt = begin; alt < end; alt++) {
> - if (alt->vendor_id != 0)
> - continue;
> -
> id = PATCH_ID_CPUFEATURE_ID(alt->patch_id);
> + vendor = PATCH_ID_CPUFEATURE_ID(alt->vendor_id);
>
> - if (id >= RISCV_ISA_EXT_MAX) {
> + /*
> + * Any alternative with a patch_id that is less than
> + * RISCV_ISA_EXT_MAX is interpreted as a standard extension.
> + *
> + * Any alternative with patch_id that is greater than or equal
> + * to RISCV_VENDOR_EXT_ALTERNATIVES_BASE is interpreted as a
> + * vendor extension.

I think this stuff is all fine, since we can always re-jig things in the
future if needs be.

> + */
> + if (id < RISCV_ISA_EXT_MAX) {
> + /*
> + * This patch should be treated as errata so skip
> + * processing here.
> + */
> + if (alt->vendor_id != 0)
> + continue;
> +
> + if (!__riscv_isa_extension_available(NULL, id))
> + continue;
> + } else if (id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE) {
> + if (!__riscv_isa_vendor_extension_available(VENDOR_EXT_ALL_CPUS, vendor, id))
> + continue;
> + } else {
> WARN(1, "This extension id:%d is not in ISA extension list", id);
> continue;
> }
>
> - if (!__riscv_isa_extension_available(NULL, id))
> - continue;
> -
> value = PATCH_ID_CPUFEATURE_VALUE(alt->patch_id);
> if (!riscv_cpufeature_patch_check(id, value))
> continue;
> diff --git a/arch/riscv/kernel/vendor_extensions.c b/arch/riscv/kernel/vendor_extensions.c
> index f76cb3013c2d..eced93eec5a6 100644
> --- a/arch/riscv/kernel/vendor_extensions.c
> +++ b/arch/riscv/kernel/vendor_extensions.c
> @@ -3,6 +3,7 @@
> * Copyright 2024 Rivos, Inc
> */
>
> +#include <asm/vendorid_list.h>
> #include <asm/vendor_extensions.h>
> #include <asm/vendor_extensions/thead.h>
>
> @@ -16,3 +17,42 @@ const struct riscv_isa_vendor_ext_data_list *riscv_isa_vendor_ext_list[] = {
> };
>
> const size_t riscv_isa_vendor_ext_list_size = ARRAY_SIZE(riscv_isa_vendor_ext_list);
> +
> +/**
> + * __riscv_isa_vendor_extension_available() - Check whether given vendor
> + * extension is available or not.
> + *
> + * @cpu: check if extension is available on this cpu
> + * @vendor: vendor that the extension is a member of
> + * @bit: bit position of the desired extension
> + * Return: true or false
> + *
> + * NOTE: When cpu is -1, will check if extension is available on all cpus
> + */
> +bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsigned int bit)
> +{
> + unsigned long *bmap;
> + struct riscv_isainfo *cpu_bmap;
> + size_t bmap_size;
> +
> + switch (vendor) {
> +#ifdef CONFIG_RISCV_ISA_VENDOR_EXT_THEAD
> + case THEAD_VENDOR_ID:
> + bmap = riscv_isa_vendor_ext_list_thead.vendor_bitmap;
> + cpu_bmap = riscv_isa_vendor_ext_list_thead.per_hart_vendor_bitmap;
> + bmap_size = riscv_isa_vendor_ext_list_thead.bitmap_size;
> + break;
> +#endif
> + default:
> + return false;
> + }
> +
> + if (cpu != -1)
> + bmap = cpu_bmap[cpu].isa;
> +
> + if (bit >= bmap_size)
> + return false;
> +
> + return test_bit(bit, bmap) ? true : false;
> +}
> +EXPORT_SYMBOL_GPL(__riscv_isa_vendor_extension_available);

I wonder if we care to implement a non __ prefixed version of this, like
the standard stuff? The only __ version users of the standard one are in
kvm and core arch code, the "external" users all use the non-prefixed
version.

In any case,
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Cheers,
Conor.

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