Re: [PATCH v3 08/17] riscv: Introduce vendor variants of extension helpers

From: Conor Dooley <conor@kernel.org>
To: Charlie Jenkins <charlie@rivosinc.com>
Cc: "Rob Herring" <robh@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Guo Ren" <guoren@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Chen-Yu Tsai" <wens@csie.org>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"Samuel Holland" <samuel@sholland.org>,
	"Conor Dooley" <conor.dooley@microchip.com>,
	"Evan Green" <evan@rivosinc.com>,
	"Clément Léger" <cleger@rivosinc.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Shuah Khan" <shuah@kernel.org>,
	linux-riscv@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Palmer Dabbelt" <palmer@rivosinc.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-doc@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 08/17] riscv: Introduce vendor variants of extension helpers
Date: Fri, 26 Apr 2024 17:19:59 +0100	[thread overview]
Message-ID: <20240426-myself-crowbar-99dc0a080cd9@spud> (raw)
In-Reply-To: <20240420-dev-charlie-support_thead_vector_6_9-v3-8-67cff4271d1d@rivosinc.com>

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On Sat, Apr 20, 2024 at 06:04:40PM -0700, Charlie Jenkins wrote:
> Vendor extensions are maintained in per-vendor structs (separate from
> standard extensions which live in riscv_isa). Create vendor variants for
> the existing extension helpers to interface with the riscv_isa_vendor
> bitmaps.

> There is a good amount of overlap between these functions, so
> the alternative checking code can be factored out.

Can you please split this out?

> 
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
>  arch/riscv/errata/sifive/errata.c          |  3 ++
>  arch/riscv/errata/thead/errata.c           |  3 ++
>  arch/riscv/include/asm/cpufeature.h        | 86 +++++++++++++++++-------------
>  arch/riscv/include/asm/vendor_extensions.h | 56 +++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c             | 20 ++++---
>  arch/riscv/kernel/vendor_extensions.c      | 40 ++++++++++++++
>  6 files changed, 164 insertions(+), 44 deletions(-)
> 
> diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
> index 3d9a32d791f7..b29b6e405ff2 100644
> --- a/arch/riscv/errata/sifive/errata.c
> +++ b/arch/riscv/errata/sifive/errata.c
> @@ -12,6 +12,7 @@
>  #include <asm/alternative.h>
>  #include <asm/vendorid_list.h>
>  #include <asm/errata_list.h>
> +#include <asm/vendor_extensions.h>
>  
>  struct errata_info_t {
>  	char name[32];
> @@ -99,6 +100,8 @@ void sifive_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  	for (alt = begin; alt < end; alt++) {
>  		if (alt->vendor_id != SIFIVE_VENDOR_ID)
>  			continue;
> +		if (alt->patch_id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE)
> +			continue;
>  		if (alt->patch_id >= ERRATA_SIFIVE_NUMBER) {
>  			WARN(1, "This errata id:%d is not in kernel errata list", alt->patch_id);
>  			continue;
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index b1c410bbc1ae..d8e78cc687bc 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -18,6 +18,7 @@
>  #include <asm/io.h>
>  #include <asm/patch.h>
>  #include <asm/vendorid_list.h>
> +#include <asm/vendor_extensions.h>
>  
>  static bool errata_probe_pbmt(unsigned int stage,
>  			      unsigned long arch_id, unsigned long impid)
> @@ -163,6 +164,8 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
>  	for (alt = begin; alt < end; alt++) {
>  		if (alt->vendor_id != THEAD_VENDOR_ID)
>  			continue;
> +		if (alt->patch_id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE)
> +			continue;

>  		if (alt->patch_id >= ERRATA_THEAD_NUMBER)

This number is 2, how does the patching actually work for vendor stuff
when the base is always greater than 2?

>  			continue;
>  
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index db6a6d7d6b2e..83e1143db9ad 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -103,22 +103,13 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, unsigned i
>  	__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
>  
>  static __always_inline bool
> -riscv_has_extension_likely(const unsigned long ext)
> +__riscv_has_extension_likely_alternatives(const unsigned long vendor, const unsigned long ext)
>  {
> -	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> -			   "ext must be < RISCV_ISA_EXT_MAX");
> -
> -	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> -		asm goto(
> -		ALTERNATIVE("j	%l[l_no]", "nop", 0, %[ext], 1)
> -		:
> -		: [ext] "i" (ext)
> -		:
> -		: l_no);
> -	} else {
> -		if (!__riscv_isa_extension_available(NULL, ext))
> -			goto l_no;
> -	}
> +	asm goto(ALTERNATIVE("j	%l[l_no]", "nop", %[vendor], %[ext], 1)
> +	:
> +	: [vendor] "i" (vendor), [ext] "i" (ext)
> +	:
> +	: l_no);
>  
>  	return true;
>  l_no:
> @@ -126,42 +117,65 @@ riscv_has_extension_likely(const unsigned long ext)
>  }
>  
>  static __always_inline bool
> -riscv_has_extension_unlikely(const unsigned long ext)
> +__riscv_has_extension_unlikely_alternatives(const unsigned long vendor, const unsigned long ext)

ngl, I think you could drop the _alternatives from these - the
likely/unlikely is only actually a thing because of the alternatives in
the first place & just retain the __ as a differentiator. That'd help
you with some of the long-line wrangling you've been doing below.

>  {
> -	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> -			   "ext must be < RISCV_ISA_EXT_MAX");
> -
> -	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> -		asm goto(
> -		ALTERNATIVE("nop", "j	%l[l_yes]", 0, %[ext], 1)
> -		:
> -		: [ext] "i" (ext)
> -		:
> -		: l_yes);
> -	} else {
> -		if (__riscv_isa_extension_available(NULL, ext))
> -			goto l_yes;
> -	}
> +	asm goto(ALTERNATIVE("nop", "j	%l[l_yes]", %[vendor], %[ext], 1)
> +	:
> +	: [vendor] "i" (vendor), [ext] "i" (ext)
> +	:
> +	: l_yes);
>  
>  	return false;
>  l_yes:
>  	return true;
>  }
>  
> +static __always_inline bool
> +riscv_has_extension_likely(const unsigned long ext)

Can you format this so that its on one line & wrap the arguments if
needs be?

> +{
> +	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> +			   "ext must be < RISCV_ISA_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_likely_alternatives(0, ext);
> +	else

I'm almost certain I said this before, but none of the else branches are
needed here, there's a return in the if branch, so the remainder of the
function becomes unconditionally executed.

> +		return __riscv_isa_extension_available(NULL, ext);
> +}
> +
> +static __always_inline bool
> +riscv_has_extension_unlikely(const unsigned long ext)
> +{
> +	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> +			   "ext must be < RISCV_ISA_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_unlikely_alternatives(0, ext);
> +	else
> +		return __riscv_isa_extension_available(NULL, ext);
> +}
> +
>  static __always_inline bool riscv_cpu_has_extension_likely(int cpu, const unsigned long ext)
>  {
> -	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_likely(ext))
> -		return true;
> +	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> +			   "ext must be < RISCV_ISA_EXT_MAX");
>  
> -	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> +	    __riscv_has_extension_likely_alternatives(0, ext))

0 is meaningless, please make this more understandable using a define of
some sort.

> +		return true;
> +	else
> +		return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
>  }
>  
>  static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsigned long ext)
>  {
> -	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_unlikely(ext))
> -		return true;
> +	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
> +			   "ext must be < RISCV_ISA_EXT_MAX");
>  
> -	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> +	    __riscv_has_extension_unlikely_alternatives(0, ext))
> +		return true;
> +	else
> +		return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
>  }
>  
>  #endif
> diff --git a/arch/riscv/include/asm/vendor_extensions.h b/arch/riscv/include/asm/vendor_extensions.h
> index 0af1ddd0af70..3e676a96016e 100644
> --- a/arch/riscv/include/asm/vendor_extensions.h
> +++ b/arch/riscv/include/asm/vendor_extensions.h
> @@ -23,4 +23,60 @@ extern const struct riscv_isa_vendor_ext_data_list *riscv_isa_vendor_ext_list[];
>  
>  extern const size_t riscv_isa_vendor_ext_list_size;
>  
> +/*
> + * The alternatives need some way of distinguishing between vendor extensions
> + * and errata. Incrementing all of the vendor extension keys so they are at
> + * least 0x8000 accomplishes that.
> + */
> +#define RISCV_VENDOR_EXT_ALTERNATIVES_BASE	0x8000
> +
> +bool __riscv_isa_vendor_extension_available(int cpu, unsigned long vendor, unsigned int bit);
> +#define riscv_cpu_isa_vendor_extension_available(cpu, vendor, ext)	\
> +	__riscv_isa_vendor_extension_available(cpu, vendor, RISCV_ISA_VENDOR_EXT_##ext)
> +#define riscv_isa_vendor_extension_available(vendor, ext)	\
> +	__riscv_isa_vendor_extension_available(-1, vendor, RISCV_ISA_VENDOR_EXT_##ext)
> +
> +static __always_inline bool
> +riscv_has_vendor_extension_likely(const unsigned long vendor, const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_likely_alternatives(vendor,
> +								 ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE);
> +	else
> +		return __riscv_isa_vendor_extension_available(-1, vendor, ext);
> +}
> +
> +static __always_inline bool
> +riscv_has_vendor_extension_unlikely(const unsigned long vendor, const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_unlikely_alternatives(vendor,
> +								   ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE);
> +	else
> +		return __riscv_isa_vendor_extension_available(-1, vendor, ext);
> +}
> +
> +static __always_inline bool riscv_cpu_has_vendor_extension_likely(const unsigned long vendor,
> +								  int cpu, const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> +	    __riscv_has_extension_likely_alternatives(vendor,
> +						      ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE))
> +		return true;
> +	else
> +		return __riscv_isa_vendor_extension_available(cpu, vendor, ext);
> +}
> +
> +static __always_inline bool riscv_cpu_has_vendor_extension_unlikely(const unsigned long vendor,
> +								    int cpu,
> +								    const unsigned long ext)
> +{
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) &&
> +	    __riscv_has_extension_unlikely_alternatives(vendor,
> +							ext + RISCV_VENDOR_EXT_ALTERNATIVES_BASE))
> +		return true;
> +	else
> +		return __riscv_isa_vendor_extension_available(cpu, vendor, ext);
> +}
> +
>  #endif /* _ASM_VENDOR_EXTENSIONS_H */
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index c9f36822e337..17371887abcc 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -833,25 +833,29 @@ 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) {
> +		if (id < RISCV_ISA_EXT_MAX) {

I think any reliance on the standard ext max requires a comment
explaining what the interaction is between it and the vendor stuff.

> +			if (alt->vendor_id != 0)
> +				continue;

If this happens, it's a bug, should we be continuing silently?

Cheers,
Conor.

> +
> +			if (!__riscv_isa_extension_available(NULL, id))
> +				continue;
> +		} else if (id >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE) {
> +			if (!__riscv_isa_vendor_extension_available(-1, 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);
> 
> -- 
> 2.44.0
> 

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