linux-kernel - Re: [PATCH 07/19] ARM64 / ACPI: Parse MADT to map logical cpu to MPIDR and get cpu_possible/present

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Message-Id: <20140820151437.91964C41290@trevor.secretlab.ca>
Date:	Wed, 20 Aug 2014 10:14:37 -0500
From:	Grant Likely <grant.likely@...aro.org>
To:	Hanjun Guo <hanjun.guo@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <mark.rutland@....com>
Cc:	Graeme Gregory <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Will Deacon <will.deacon@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...aro.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles.Garcia-Tobin@....com, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-acpi-private@...aro.org, Hanjun Guo <hanjun.guo@...aro.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Subject: Re: [PATCH 07/19] ARM64 / ACPI: Parse MADT to map logical cpu to
 MPIDR and get cpu_possible/present_map

On Thu, 24 Jul 2014 21:00:13 +0800, Hanjun Guo <hanjun.guo@...aro.org> wrote:
> MADT contains the information for MPIDR which is essential for
> SMP initialization, parse the GIC cpu interface structures to
> get the MPIDR value and map it to cpu_logical_map(), and add
> enabled cpu with valid MPIDR into cpu_possible_map and
> cpu_present_map.
> 
> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...aro.org>
> ---
> +	/* If it is the first CPU, no need to check duplicate MPIDRs */
> +	if (!enabled_cpus)
> +		goto skip_mpidr_check;
> +
> +	/*
> +	 * Duplicate MPIDRs are a recipe for disaster. Scan
> +	 * all initialized entries and check for
> +	 * duplicates. If any is found just ignore the CPU.
> +	 */
> +	for_each_present_cpu(cpu) {
> +		if (cpu_logical_map(cpu) == mpidr) {
> +			pr_err("Firmware bug, duplicate CPU MPIDR: 0x%llx in MADT\n",
> +			       mpidr);
> +			return -EINVAL;
> +		}
> +	}
> +
> +skip_mpidr_check:
> +	enabled_cpus++;

So, this hunk is embarrasing. The goto is completely unnecessary and the
whole for_each_present_cpu() block can be inside an
"if (enabled_cpus) { ... }" block. A goto is just nasty.

That said, is the if even necessary? Will for_each_present_cpu() iterate
over anything if it is processing the first cpu? (I don't actually know
the answer here, I did a quick look but not enough to get an
authoritative answer).

g.
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