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Date: Fri, 12 Apr 2024 12:49:57 +0100
From: Conor Dooley <conor.dooley@microchip.com>
To: Charlie Jenkins <charlie@rivosinc.com>
CC: Conor Dooley <conor@kernel.org>, 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>, Evan Green
	<evan@rivosinc.com>, =?iso-8859-1?Q?Cl=E9ment_L=E9ger?=
	<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 08/19] riscv: Introduce vendor variants of extension
 helpers
Message-ID: <20240412-dwarf-shower-5a7300fcd283@wendy>
References: <20240411-dev-charlie-support_thead_vector_6_9-v1-0-4af9815ec746@rivosinc.com>
 <20240411-dev-charlie-support_thead_vector_6_9-v1-8-4af9815ec746@rivosinc.com>
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On Thu, Apr 11, 2024 at 09:11:14PM -0700, Charlie Jenkins wrote:
> Create vendor variants of the existing extension helpers. If the
> existing functions were instead modified to support vendor extensions, a
> branch based on the ext value being greater than
> RISCV_ISA_VENDOR_EXT_BASE would have to be introduced. This additional
> branch would have an unnecessary performance impact.
>=20
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>

I've not looked at the "main" patch in the series that adds all of the
probing and structures for representing this info yet beyond a cursory
glance, but it feels like we're duplicating a bunch of infrastructure
here before it is necessary. The IDs are all internal to Linux, so I'd
rather we kept everything in the same structure until we have more than
a handful of vendor extensions. With this patch (and the theadpmu stuff)
we will have three vendor extensions which feels like a drop in the
bucket compared to the standard ones.


> ---
>  arch/riscv/include/asm/cpufeature.h | 54 +++++++++++++++++++++++++++++++=
++++++
>  arch/riscv/kernel/cpufeature.c      | 34 ++++++++++++++++++++---
>  2 files changed, 84 insertions(+), 4 deletions(-)
>=20
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm=
/cpufeature.h
> index db2ab037843a..8f19e3681b4f 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -89,6 +89,10 @@ bool __riscv_isa_extension_available(const unsigned lo=
ng *isa_bitmap, unsigned i
>  #define riscv_isa_extension_available(isa_bitmap, ext)	\
>  	__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
> =20
> +bool __riscv_isa_vendor_extension_available(const unsigned long *vendor_=
isa_bitmap, unsigned int bit);
> +#define riscv_isa_vendor_extension_available(isa_bitmap, ext)	\
> +	__riscv_isa_vendor_extension_available(isa_bitmap, RISCV_ISA_VENDOR_EXT=
_##ext)
> +
>  static __always_inline bool
>  __riscv_has_extension_likely_alternatives(const unsigned long ext)
>  {
> @@ -117,6 +121,8 @@ __riscv_has_extension_unlikely_alternatives(const uns=
igned long ext)
>  	return true;
>  }
> =20
> +/* Standard extension helpers */
> +
>  static __always_inline bool
>  riscv_has_extension_likely(const unsigned long ext)
>  {
> @@ -163,4 +169,52 @@ static __always_inline bool riscv_cpu_has_extension_=
unlikely(int cpu, const unsi
>  		return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
>  }
> =20
> +/* Vendor extension helpers */
> +
> +static __always_inline bool
> +riscv_has_vendor_extension_likely(const unsigned long ext)
> +{
> +	compiletime_assert(ext < RISCV_ISA_VENDOR_EXT_MAX,
> +			   "ext must be < RISCV_ISA_VENDOR_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_likely_alternatives(ext);
> +	else
> +		return __riscv_isa_vendor_extension_available(NULL, ext);
> +}
> +
> +static __always_inline bool
> +riscv_has_vendor_extension_unlikely(const unsigned long ext)
> +{
> +	compiletime_assert(ext < RISCV_ISA_VENDOR_EXT_MAX,
> +			   "ext must be < RISCV_ISA_VENDOR_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_unlikely_alternatives(ext);
> +	else
> +		return __riscv_isa_vendor_extension_available(NULL, ext);
> +}
> +
> +static __always_inline bool riscv_cpu_has_vendor_extension_likely(int cp=
u, const unsigned long ext)
> +{
> +	compiletime_assert(ext < RISCV_ISA_VENDOR_EXT_MAX,
> +			   "ext must be < RISCV_ISA_VENDOR_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_likely_alternatives(ext);
> +	else
> +		return __riscv_isa_vendor_extension_available(hart_isa_vendor[cpu].isa=
, ext);
> +}
> +
> +static __always_inline bool riscv_cpu_has_vendor_extension_unlikely(int =
cpu, const unsigned long ext)
> +{
> +	compiletime_assert(ext < RISCV_ISA_VENDOR_EXT_MAX,
> +			   "ext must be < RISCV_ISA_VENDOR_EXT_MAX");
> +
> +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE))
> +		return __riscv_has_extension_unlikely_alternatives(ext);
> +	else
> +		return __riscv_isa_vendor_extension_available(hart_isa_vendor[cpu].isa=
, ext);
> +}

Same stuff about constant folding applies to these, I think these should
just mirror the existing functions (if needed at all).

Cheers,
Conor.

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