Blackfin: SMP: don't start up core b until its state has been completely onlined

When testing PREEMPT_RT kernel on BF561-EZKit, the kernel blocks while
booting.  When the kernel initializes the ethernet driver, it sleeps and
never wakes up.

The issue happens when the kernel waits for a timer for Core B to timeout
(the timers are per-cpu based: static DEFINE_PER_CPU(struct tvec_base *,
tvec_bases) = &boot_tvec_bases).

However, the ksoftirqd thread for Core B (note, the ksoftirqd thread is
also per-cpu based) cannot work properly, and the timers for Core B never
times out.

When ksoftirqd() for the first time runs on core B, it is possible core A
is still initializing core B (see smp_init() -> cpu_up() -> __cpu_up()).
So the "cpu_is_offline()" check may return true and ksoftirqd moves to
"wait_to_die".

So delay the core b start up until the per-cpu timers have been set up
fully.

Signed-off-by: Yi Li <yi.li@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 7 insertions, 10 deletions

diff --git a/arch/blackfin/mach-bf561/smp.c b/arch/blackfin/mach-bf561/smp.c
index 510f57641495..0192532e96a2 100644
--- a/arch/blackfin/mach-bf561/smp.c
+++ b/arch/blackfin/mach-bf561/smp.c
@@ -52,8 +52,6 @@ int __init setup_profiling_timer(unsigned int multiplier) /* not supported */
 
 void __cpuinit platform_secondary_init(unsigned int cpu)
 {
-        local_irq_disable();
-
         /* Clone setup for peripheral interrupt sources from CoreA. */
         bfin_write_SICB_IMASK0(bfin_read_SICA_IMASK0());
         bfin_write_SICB_IMASK1(bfin_read_SICA_IMASK1());
@@ -70,11 +68,6 @@ void __cpuinit platform_secondary_init(unsigned int cpu)
         bfin_write_SICB_IAR7(bfin_read_SICA_IAR7());
         SSYNC();
 
-        local_irq_enable();
-
-        /* Calibrate loops per jiffy value. */
-        calibrate_delay();
-
         /* Store CPU-private information to the cpu_data array. */
         bfin_setup_cpudata(cpu);
 
@@ -108,9 +101,13 @@ int __cpuinit platform_boot_secondary(unsigned int cpu, struct task_struct *idle
                 barrier();
         }
 
-        spin_unlock(&boot_lock);
-
-        return cpu_isset(cpu, cpu_callin_map) ? 0 : -ENOSYS;
+        if (cpu_isset(cpu, cpu_callin_map)) {
+                cpu_set(cpu, cpu_online_map);
+                /* release the lock and let coreb run */
+                spin_unlock(&boot_lock);
+                return 0;
+        } else
+                panic("CPU%u: processor failed to boot\n", cpu);
 }
 
 void __init platform_request_ipi(irq_handler_t handler)