Re: [PATCH 1/8] ARM: SCU: Add common routines for secondary CPU bootup

Russell King - ARM Linux
2010-11-30T23:32:04Z

On Tue, Nov 30, 2010 at 08:16:58PM +0300, Anton Vorontsov wrote:
> +/*
> + * Initialise the CPU possible map early - this describes the CPUs
> + * which may be present or become present in the system.
> + */
> +void __init scu_init_cpus(void __iomem *scu_base)
> +{
> + unsigned int ncores = scu_base ? scu_get_core_count(scu_base) : 1;
> + unsigned int i;
> +
> + /* sanity check */
> + if (ncores == 0) {
> + pr_err("%s: strange CM count of 0? Default to 1\n", __func__);
> + ncores = 1;
> + }
> +
> + if (ncores > NR_CPUS) {
> + pr_warn("%s: no. of cores (%d) greater than configured "
> + "maximum of %d - clipping\n", __func__, ncores, NR_CPUS);
> + ncores = NR_CPUS;
> + }
> +
> + for (i = 0; i < ncores; i++)
> + set_cpu_possible(i, true);
> +}
> +
> +void __init scu_prepare_cpus(void __iomem *scu_base, unsigned int max_cpus)
> +{
> + unsigned int ncores = num_possible_cpus();
> + unsigned int cpu = smp_processor_id();
> + int i;
> +
> + smp_store_cpu_info(cpu);
> +
> + /*
> + * are we trying to boot more cores than exist?
> + */
> + if (max_cpus > ncores)
> + max_cpus = ncores;
> +
> + /*
> + * 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);
> +
> + /*
> + * Initialise the SCU if there are more than one CPU and let
> + * them know where to start.
> + */
> + if (max_cpus > 1) {
> + /*
> + * Enable the local timer or broadcast device for the
> + * boot CPU, but only if we have more than one CPU.
> + */
> + percpu_timer_setup();
> +
> + scu_enable(scu_base);
> + }
> +}

Note that I'll go with factoring this out into arch/arm/kernel/smp_scu.c
for the time being, but I'm not convinced about the other parts yet.

> + sub r4, r4, r5
> + add r6, r6, r4
> +#if __LINUX_ARM_ARCH__ >= 7
> + dsb
> +#endif

Another question though - probably for Linus though - why is the u8500
code needing this dsb whereas other ARMv7 implementations don't appear
to require it?