linux-kernel - Re: [PATCH 1/4] Add smp support for Allwinner A20(sunxi 7i).

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Date:	Thu, 12 Sep 2013 15:40:08 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Fan Rong <cinifr@...il.com>
Cc:	coosty@....com, maxime.ripard@...e-electrons.com,
	daniel.lezcano@...aro.org, tglx@...utronix.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mark.rutland@....com, pawel.moll@....co, rob.herring@...xeda.com,
	linux-sunxi@...glegroups.com
Subject: Re: [PATCH 1/4] Add smp support for Allwinner A20(sunxi 7i).

Some other comments:

On Thu, Sep 12, 2013 at 02:51:24PM +0800, Fan Rong wrote:
> +    /* L1RSTDISABLE hold low */
> +	pwr_reg = readl(cc_base + AW_CPUCFG_GENCTL);
> +	pwr_reg &= ~(1<<cpu);

If you pass your patch through checkpatch.pl, it will warn about some of
this.  You should have one space each side of <<.

> +    /* step3: clear power-off gating */
> +	pwr_reg = readl(cc_base + AW_CPU1_PWROFF_REG);
> +	pwr_reg &= ~(1);

You don't need the parens here.

> +	pwr_reg = readl(cc_base + AW_CPUCFG_DBGCTL1);
> +	pwr_reg |= (1<<cpu);

Nor here.

> +static int sunxi7i_boot_secondary(unsigned int cpu, struct task_struct *idle)
> +{
> +	pr_debug("[%s] enter cpu %d\n", __func__, cpu);
> +	spin_lock(&boot_lock);
> +	enable_aw_cpu(cpu);
> +	spin_unlock(&boot_lock);

What exactly does this spinlock protect?  The core code already provides
the guarantee that only one CPU will be brought online or taken offline
at a time.
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