linux-kernel - Re: [PATCH 1/2] riscv: cpufeature: Fix thead vector hwcap removal

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Message-ID: <20240426-d8aba0211e882568ccc761df@orel>
Date: Fri, 26 Apr 2024 11:02:30 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: 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@...nel.org>, Conor Dooley <conor.dooley@...rochip.com>, 
	Clément Léger <cleger@...osinc.com>, Evan Green <evan@...osinc.com>, 
	Palmer Dabbelt <palmer@...osinc.com>, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: cpufeature: Fix thead vector hwcap removal

On Wed, Apr 24, 2024 at 09:19:54AM GMT, Charlie Jenkins wrote:
..
> +	/*
> +	 * Naively assume that all harts have the same mvendorid/marchid as the
> +	 * boot hart.

This comment isn't necessary, since we don't have to assume all harts have
the same IDs. This information is currently being collected specifically
for thead. So, we can state in a comment below, where the information is
used, that we assume when the boot hart is thead, then we don't want to
enable V on any hart (whatever their IDs are).

Thanks,
drew

> +	 */
> +	boot_vendorid = riscv_get_mvendorid();
> +	boot_archid = riscv_get_marchid();
> +
>  	for_each_possible_cpu(cpu) {
>  		struct riscv_isainfo *isainfo = &hart_isa[cpu];
>  		unsigned long this_hwcap = 0;
> @@ -544,8 +553,7 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  		 * CPU cores with the ratified spec will contain non-zero
>  		 * marchid.
>  		 */
> -		if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID &&
> -		    riscv_cached_marchid(cpu) == 0x0) {
> +		if (acpi_disabled && boot_vendorid == THEAD_VENDOR_ID && boot_archid == 0x0) {
>  			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
>  			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
>  		}
> 
> -- 
> 2.44.0
> 
> 
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> linux-riscv@...ts.infradead.org
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