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

From: Charlie Jenkins <charlie@rivosinc.com>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: "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@kernel.org>,
	"Conor Dooley" <conor.dooley@microchip.com>,
	"Clément Léger" <cleger@rivosinc.com>,
	"Evan Green" <evan@rivosinc.com>,
	"Palmer Dabbelt" <palmer@rivosinc.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] riscv: cpufeature: Fix thead vector hwcap removal
Date: Fri, 26 Apr 2024 14:30:37 -0700	[thread overview]
Message-ID: <Ziwc/SnWVITvsFgZ@ghost> (raw)
In-Reply-To: <20240426-d8aba0211e882568ccc761df@orel>

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
> > 
> > 
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