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

[Charlie Jenkins <charlie@rivosinc.com>]

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.