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

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Message-ID: <20240501-tripping-acetone-e556e993ba95@spud>
Date: Wed, 1 May 2024 12:29:56 +0100
From: Conor Dooley <conor@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Evan Green <evan@...osinc.com>,
	Clément Léger <cleger@...osinc.com>,
	Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
	linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 06/16] riscv: Introduce vendor variants of extension
 helpers

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@...rochip.com>

Cheers,
Conor.

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