[PATCH 2/3] ARM: Xilinx: add SMP specific support files

[catalin.marinas@arm.com (Catalin Marinas)]

John,

A few suggestions on barriers below.

On 3 April 2011 22:00, John Linn <john.linn@xilinx.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