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

Charlie Jenkins
2024-05-01T19:45:46Z

On Wed, May 01, 2024 at 12:29:56PM +0100, Conor Dooley wrote:
> 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 vendor_extensions.h there is:

#define riscv_isa_vendor_extension_available(vendor, ext) \
__riscv_isa_vendor_extension_available(VENDOR_EXT_ALL_CPUS, vendor, \
RISCV_ISA_VENDOR_EXT_##ext)

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

Thanks!

- Charlie

>
> Cheers,
> Conor.