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

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Message-ID: <Ziwc/SnWVITvsFgZ@ghost>
Date: Fri, 26 Apr 2024 14:30:37 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.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 Fri, Apr 26, 2024 at 11:02:30AM +0200, Andrew Jones wrote:
> 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).

Yes you are correct, I will do as you suggest.

- Charlie

> 
> 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
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv

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