target/linux/brcm2708/patches-4.14/950-0010-irq_bcm2836-Send-event-when-onlining-sleeping-cores.patch

   1 From 6b8b69ff7c4c25f01535cbe49a80516df6dbcfe8 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Mon, 8 May 2017 16:43:40 +0100
   4 Subject: [PATCH 010/454] irq_bcm2836: Send event when onlining sleeping cores
   5
   6 In order to reduce power consumption and bus traffic, it is sensible
   7 for secondary cores to enter a low-power idle state when waiting to
   8 be started. The wfe instruction causes a core to wait until an event
   9 or interrupt arrives before continuing to the next instruction.
  10 The sev instruction sends a wakeup event to the other cores, so call
  11 it from bcm2836_smp_boot_secondary, the function that wakes up the
  12 waiting cores during booting.
  13
  14 It is harmless to use this patch without the corresponding change
  15 adding wfe to the ARMv7/ARMv8-32 stubs, but if the stubs are updated
  16 and this patch is not applied then the other cores will sleep forever.
  17
  18 See: https://github.com/raspberrypi/linux/issues/1989
  19
  20 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  21 ---
  22  drivers/irqchip/irq-bcm2836.c | 3 +++
  23  1 file changed, 3 insertions(+)
  24
  25 --- a/drivers/irqchip/irq-bcm2836.c
  26 +++ b/drivers/irqchip/irq-bcm2836.c
  27 @@ -227,6 +227,9 @@ static int __init bcm2836_smp_boot_secon
  28         writel(secondary_startup_phys,
  29                intc.base + LOCAL_MAILBOX3_SET0 + 16 * cpu);
  30
  31 +       dsb(sy); /* Ensure write has completed before waking the other CPUs */
  32 +       sev();
  33 +
  34         return 0;
  35  }
  36