Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
Date:   Tue, 19 Sep 2023 11:24:41 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc:     James Morse <james.morse@arm.com>, linux-pm@vger.kernel.org,
        loongarch@lists.linux.dev, linux-acpi@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev,
        x86@kernel.org, Salil Mehta <salil.mehta@huawei.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        jianyong.wu@arm.com, justin.he@arm.com
Subject: Re: [RFC PATCH v2 32/35] ACPI: add support to register CPUs based on
 the _STA enabled bit
Message-ID: <ZQl26YlRnQaKwCg6@shell.armlinux.org.uk>
References: <20230913163823.7880-1-james.morse@arm.com>
 <20230913163823.7880-33-james.morse@arm.com>
 <20230914171341.00006e51@Huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230914171341.00006e51@Huawei.com>
Sender: Russell King (Oracle) <linux@armlinux.org.uk>
Precedence: bulk

On Thu, Sep 14, 2023 at 05:13:41PM +0100, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:20 +0000
> James Morse <james.morse@arm.com> wrote:
> > +static int acpi_processor_make_enabled(struct acpi_processor *pr)
> > +{
> > +	unsigned long long sta;
> > +	acpi_status status;
> > +	bool present, enabled;
> > +
> > +	if (!acpi_has_method(pr->handle, "_STA"))
> > +		return arch_register_cpu(pr->id);
> > +
> > +	status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
> > +	if (ACPI_FAILURE(status))
> > +		return -ENODEV;
> > +
> > +	present = sta & ACPI_STA_DEVICE_PRESENT;
> > +	enabled = sta & ACPI_STA_DEVICE_ENABLED;
> > +
> > +	if (cpu_online(pr->id) && (!present || !enabled)) {
> > +		pr_err_once(FW_BUG "CPU %u is online, but described as not present or disabled!\n", pr->id);
> 
> Why once?  If this for some reason happened on multiple CPUs I think we'd want to know.
> 
> > +		add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
> > +	} else if (!present || !enabled) {
> > +		return -ENODEV;
> > +	}
> 
> I guess you didn't do a nested if here to avoid even longer lines.
> Could flip things around though I don't like this much either as it makes
> the normal good path exit mid way down.
> 
> 	if (present && enabled)
> 		return arch_register_cpu(pr->id);
> 
> 	if (!cpu_online(pr->id))
> 		return -ENODEV;
> 
> 	pr_err...
> 	add_taint(...
> 
> 	return arch_register_cpu(pr->id);
> 
> Ah well. Some code just has to be less than pretty.

How about:

static int acpi_processor_should_register_cpu(struct acpi_processor *pr)
{
	unsigned long long sta;
	acpi_status status;

	if (!acpi_has_method(pr->handle, "_STA"))
		return 0;

	status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
	if (ACPI_FAILURE(status))
		return -ENODEV;

	if (sta & ACPI_STA_DEVICE_PRESENT && sta & ACPI_STA_DEVICE_ENABLED)
		return 0;

	if (cpu_online(pr->id)) {
		pr_err_once(FW_BUG
			    "CPU %u is online, but described as not present or disabled!\n",
			    pr->id);

		/* Register the CPU anyway */
		return 0;
	}

	return -ENODEV;
}

static int acpi_processor_make_enabled(struct acpi_processor *pr)
{
	int ret = acpi_processor_should_register_cpu(pr);

	if (ret)
		return ret;

	return arch_register_cpu(pr->id);
}

I would keep the "cpu online but !present and !disabled" as a sub-block
because it makes better reading flow, but instead break the message as
I've indicated above.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!