Re: [PATCH 1/2] ARM: oxnas: Add OX820 SMP support

From: Arnd Bergmann
Date: Mon Oct 17 2016 - 05:07:08 EST


On Monday, October 17, 2016 10:43:02 AM CEST Neil Armstrong wrote:
> +
> + /*
> + * This is really belt and braces; we hold unintended secondary
> + * CPUs in the holding pen until we're ready for them. However,
> + * since we haven't sent them a soft interrupt, they shouldn't
> + * be there.
> + */
> + write_pen_release(cpu);
> +
> + /*
> + * Enable GIC cpu interface in CPU Interface Control Register
> + */
> + writel(GIC_CPU_CTRL_ENABLE,
> + gic_cpu_ctrl + GIC_NCPU_OFFSET(cpu) + GIC_CPU_CTRL);
> +
> + /*
> + * Send the secondary CPU a soft interrupt, thereby causing
> + * the boot monitor to read the system wide flags register,
> + * and branch to the address found there.
> + */
> +
> + arch_send_wakeup_ipi_mask(cpumask_of(cpu));
> + timeout = jiffies + (1 * HZ);
> + while (time_before(jiffies, timeout)) {
> + smp_rmb();
> + if (read_pen_release() == -1)
> + break;
> +
> + udelay(10);
> + }
>

This seems to have been copied from plat-versatile, but is really
not needed here since you apparently have proper hardware support for
starting up the CPUs.

Any reason you can't just write to the cpu_ctrl register
once and keep going without that whole holding_pen loop
and spinlock?

Arnd