linux-kernel - Re: [PATCH 2/3] ARM: Xilinx: add SMP specific support files

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Date:	Mon, 4 Apr 2011 16:13:25 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	John Linn <john.linn@...inx.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux@....linux.org.uk, glikely@...retlab.ca, jamie@...ieiles.com,
	arnd@...db.de
Subject: Re: [PATCH 2/3] ARM: Xilinx: add SMP specific support files

John,

A few suggestions on barriers below.

On 3 April 2011 22:00, John Linn <john.linn@...inx.com> wrote:
> diff --git a/arch/arm/mach-xilinx/platsmp.c b/arch/arm/mach-xilinx/platsmp.c
> new file mode 100644
> index 0000000..be2d55c
> --- /dev/null
> +++ b/arch/arm/mach-xilinx/platsmp.c
...
> +int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle)
> +{
> +       unsigned long timeout;
> +
> +       /*
> +        * set synchronisation state between this boot processor
> +        * and the secondary one
> +        */
> +       spin_lock(&boot_lock);
> +
> +       printk(KERN_INFO "Xilinx SMP: booting CPU1 now\n");
> +
> +       /*
> +        * Update boot lock register with the boot key to allow the
> +        * secondary processor to start the kernel after an SEV.
> +        */
> +       __raw_writel(BOOT_LOCK_KEY, OCM_HIGH_BASE + BOOT_LOCK_OFFSET);
> +
> +       /* Flush the kernel cache to ensure that the page tables are
> +        * available for the secondary CPU to use and make sure that
> +        * the write buffer is drained before doing an SEV.
> +        */
> +       flush_cache_all();
> +       smp_wmb();
> +
> +       /*
> +        * Send an event to wake the secondary core from WFE state.
> +        */
> +       sev();

You could flush the cache before writing the boot lock register in
case the secondary wakes up from WFE. You also need a wmb() rather
than the smp_wmb(). The latter only works in the inner shareable
domain but the secondary CPU hasn't initialised the MMU yet.

Something like below:

flush_cache_all();
__raw_writel(BOOT_LOCK_KEY, OCM_HIGH_BASE + BOOT_LOCK_OFFSET);
mb();
sev();

> +void __init platform_smp_prepare_cpus(unsigned int max_cpus)
> +{
> +       int i;
> +
> +       /*
> +        * Initialise the present map, which describes the set of CPUs
> +        * actually populated at the present time.
> +        */
> +       for (i = 0; i < max_cpus; i++)
> +               set_cpu_present(i, true);
> +
> +       scu_enable(scu_base);
> +
> +       /* Initialize the boot lock register to prevent CPU1 from
> +          starting the kernel before CPU0 is ready for that.
> +       */
> +       __raw_writel(0, OCM_HIGH_BASE + BOOT_LOCK_OFFSET);
> +
> +       /*
> +        * Write the address of secondary startup routine into the
> +        * boot address. The secondary CPU will use this value
> +        * to get into the kernel after it's awake from WFE state.
> +        *
> +        * Note the physical address is needed as the secondary CPU
> +        * will not have the MMU on yet. A barrier is added to ensure
> +        * that write buffer is drained.
> +        */
> +       __raw_writel(virt_to_phys(xilinx_secondary_startup),
> +                                       OCM_HIGH_BASE + BOOT_ADDR_OFFSET);
> +       smp_wmb();

Same here, use a wmb() or mb() before the sev().

-- 
Catalin
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