Re: [PATCH V4 12/23] RISC-V: cpufeature: Avoid calling riscv_of_processor_hartid()

From: Conor Dooley <conor@kernel.org>
To: Sunil V L <sunilvl@ventanamicro.com>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-acpi@vger.kernel.org,
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	platform-driver-x86@vger.kernel.org, llvm@lists.linux.dev,
	Weili Qian <qianweili@huawei.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Tom Rix <trix@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
	Marc Zyngier <maz@kernel.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Mark Gross <markgross@kernel.org>,
	Hans de Goede <hdegoede@redhat.com>,
	Zhou Wang <wangzhou1@hisilicon.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Maximilian Luz <luzmaximilian@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Len Brown <lenb@kernel.org>
Subject: Re: [PATCH V4 12/23] RISC-V: cpufeature: Avoid calling riscv_of_processor_hartid()
Date: Tue, 4 Apr 2023 21:46:54 +0100	[thread overview]
Message-ID: <20230404-pavestone-skinless-2f466941a95b@spud> (raw)
In-Reply-To: <20230404182037.863533-13-sunilvl@ventanamicro.com>

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On Tue, Apr 04, 2023 at 11:50:26PM +0530, Sunil V L wrote:
> riscv_fill_hwcap() finds hartid of each cpu but never really uses
> it. So, remove this unnecessary call.

"Never uses it" or "never really uses it"?
This commit message misses the point though I think - is this here to
get the hartid, or is it here to do all the property validation that
riscv_of_processor_hartid() does for a cpu node?

This was added all the way back in 4.20 in commit 732e8e4130ff ("RISC-V:
properly determine hardware caps").
As the loop is a for_each_of_cpu_node(), I don't think this change is
actually valid - there's no guarantee that the cpu we are iterating over
is actually available and the riscv_of_processor_hartid() check is used
to skip "bad" cpus AFAICT.

Perhaps I am missing something, I don't think you can do this until you
switch the loop to use something that only uses cpus that you know are
valid.

Cheers,
Conor.

> Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> ---
>  arch/riscv/kernel/cpufeature.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 59d58ee0f68d..63e56ce04162 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -91,7 +91,6 @@ void __init riscv_fill_hwcap(void)
>  	char print_str[NUM_ALPHA_EXTS + 1];
>  	int i, j, rc;
>  	unsigned long isa2hwcap[26] = {0};
> -	unsigned long hartid;
>  
>  	isa2hwcap['i' - 'a'] = COMPAT_HWCAP_ISA_I;
>  	isa2hwcap['m' - 'a'] = COMPAT_HWCAP_ISA_M;
> @@ -109,10 +108,6 @@ void __init riscv_fill_hwcap(void)
>  		DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
>  		const char *temp;
>  
> -		rc = riscv_of_processor_hartid(node, &hartid);
> -		if (rc < 0)
> -			continue;
> -
>  		if (of_property_read_string(node, "riscv,isa", &isa)) {
>  			pr_warn("Unable to find \"riscv,isa\" devicetree entry\n");
>  			continue;
> -- 
> 2.34.1
> 
> 
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