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

[John Linn]

> -----Original Message-----
> From: catalin.marinas at gmail.com [mailto:catalin.marinas at gmail.com] On
> Behalf Of Catalin Marinas
> Sent: Monday, April 04, 2011 9:13 AM
> To: John Linn
> Cc: linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org;
> linux at arm.linux.org.uk; glikely at secretlab.ca; jamie at jamieiles.com;
> arnd at arndb.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 at 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. 

Understood. Since we control when it gets into the kernel completely I guess I wasn't worried about it, maybe I should have been.  Easy enough to change, not a big deal.

> 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.

Ok, great, appreciate the help there.

> 
> 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().
> 

Yes.

Thanks for the input and taking time to review.  I'll wait a bit to see if any 
other input before spinning a new patch set.

-- John

> --
> Catalin


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