linux-kernel - Re: [PATCH 2/4] irqchip: bcm2836: Add SMP support for the 2836

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Date:	Sat, 2 Jan 2016 10:27:47 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Eric Anholt <eric@...olt.net>
Cc:	linux-rpi-kernel@...ts.infradead.org,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
	Andrea Merello <andrea.merello@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/4] irqchip: bcm2836: Add SMP support for the 2836

On Sat, Dec 26, 2015 at 01:47:22PM -0800, Eric Anholt wrote:
> +int __init bcm2836_smp_boot_secondary(unsigned int cpu,
> +				      struct task_struct *idle)
> +{
> +	unsigned long secondary_startup_phys =
> +		(unsigned long)virt_to_phys((void *)secondary_startup);
> +
> +	dsb();
> +	writel(secondary_startup_phys,
> +	       intc.base + LOCAL_MAILBOX3_SET0 + 16 * cpu);

Please explain why you need this dsb() - I can't see a reason for it.
writel() has a barrier internally prior to writing the register, and
therefore I think the above dsb() is entirely redundant.

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