linux-kernel - Re: [PATCH 15/19] riscv: hwcap: Add v to hwcap if xtheadvector enabled

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Message-ID: <20240412-thrill-amnesty-019897f21466@wendy>
Date: Fri, 12 Apr 2024 12:37:08 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
To: Charlie Jenkins <charlie@...osinc.com>
CC: Conor Dooley <conor@...nel.org>, 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>, 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 15/19] riscv: hwcap: Add v to hwcap if xtheadvector
 enabled

On Thu, Apr 11, 2024 at 09:11:21PM -0700, Charlie Jenkins wrote:
> xtheadvector is not vector 1.0 compatible, but it can leverage all of
> the same save/restore routines as vector plus
> riscv_v_first_use_handler(). vector 1.0 and xtheadvector are mutually
> exclusive so there is no risk of overlap.

I think this not okay to do - if a program checks hwcap to see if vector
is supported they'll get told it is on T-Head system where only the 0.7.1
is.

> 
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
>  arch/riscv/kernel/cpufeature.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 41a4d2028428..59f628b1341c 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -647,9 +647,13 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  		 * Many vendors with T-Head CPU cores which implement the 0.7.1
>  		 * version of the vector specification put "v" into their DTs.
>  		 * CPU cores with the ratified spec will contain non-zero
> -		 * marchid.
> +		 * marchid. Only allow "v" to be set if xtheadvector is present.
>  		 */
> -		if (acpi_disabled && this_vendorid == THEAD_VENDOR_ID &&
> +		if (__riscv_isa_vendor_extension_available(isavendorinfo->isa,
> +							   RISCV_ISA_VENDOR_EXT_XTHEADVECTOR)) {
> +			this_hwcap |= isa2hwcap[RISCV_ISA_EXT_v];
> +			set_bit(RISCV_ISA_EXT_v, isainfo->isa);
> +		} else if (acpi_disabled && this_vendorid == THEAD_VENDOR_ID &&
>  		    this_archid == 0x0) {
>  			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
>  			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
> @@ -776,6 +780,15 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
>  
>  		of_node_put(cpu_node);
>  
> +		/*
> +		 * Enable kernel vector routines if xtheadvector is present
> +		 */
> +		if (__riscv_isa_vendor_extension_available(isavendorinfo->isa,
> +							   RISCV_ISA_VENDOR_EXT_XTHEADVECTOR)) {
> +			this_hwcap |= isa2hwcap[RISCV_ISA_EXT_v];
> +			set_bit(RISCV_ISA_EXT_v, isainfo->isa);
> +		}
> +
>  		/*
>  		 * All "okay" harts should have same isa. Set HWCAP based on
>  		 * common capabilities of every "okay" hart, in case they don't.
> 
> -- 
> 2.44.0
> 

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