Hi Greg and Shawn,

The patch below does not apply to the 3.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Could you please confirm?

Regards, Kohji Okuno

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From 6000156db44bbdae0bd720c46e68a2622639d9d8 Mon Sep 17 00:00:00 2001

From: Kohji Okuno okuno.kohji@jp.panasonic.com Date: Mon, 1 Apr 2019 14:22:02 +0900 Subject: [PATCH] ARM: imx6q: cpuidle: fix bug that CPU might not wake up at expected time

commit 91740fc8242b4f260cfa4d4536d8551804777fae upstream.

In the current cpuidle implementation for i.MX6q, the CPU that sets 'WAIT_UNCLOCKED' and the CPU that returns to 'WAIT_CLOCKED' are always the same. While the CPU that sets 'WAIT_UNCLOCKED' is in IDLE state of "WAIT", if the other CPU wakes up and enters IDLE state of "WFI" istead of "WAIT", this CPU can not wake up at expired time. Because, in the case of "WFI", the CPU must be waked up by the local timer interrupt. But, while 'WAIT_UNCLOCKED' is set, the local timer is stopped, when all CPUs execute "wfi" instruction. As a result, the local timer interrupt is not fired. In this situation, this CPU will wake up by IRQ different from local timer. (e.g. broacast timer)

So, this fix changes CPU to return to 'WAIT_CLOCKED'.

Signed-off-by: Kohji Okuno okuno.kohji@jp.panasonic.com Fixes: e5f9dec8ff5f ("ARM: imx6q: support WAIT mode using cpuidle") Cc: stable@vger.kernel.org Signed-off-by: Shawn Guo shawnguo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

[okuno.kohji: backport to 3.18]

Signed-off-by: Kohji Okuno okuno.kohji@jp.panasonic.com --- arch/arm/mach-imx/cpuidle-imx6q.c | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/arch/arm/mach-imx/cpuidle-imx6q.c b/arch/arm/mach-imx/cpuidle-imx6q.c index aa935787b743..9d219b626949 100644 --- a/arch/arm/mach-imx/cpuidle-imx6q.c +++ b/arch/arm/mach-imx/cpuidle-imx6q.c @@ -15,30 +15,23 @@ #include "cpuidle.h" #include "hardware.h"

-static atomic_t master = ATOMIC_INIT(0); -static DEFINE_SPINLOCK(master_lock); +static int num_idle_cpus = 0; +static DEFINE_SPINLOCK(cpuidle_lock);

static int imx6q_enter_wait(struct cpuidle_device *dev, struct cpuidle_driver *drv, int index) { - if (atomic_inc_return(&master) == num_online_cpus()) { - /* - * With this lock, we prevent other cpu to exit and enter - * this function again and become the master. - */ - if (!spin_trylock(&master_lock)) - goto idle; + spin_lock(&cpuidle_lock); + if (++num_idle_cpus == num_online_cpus()) imx6q_set_lpm(WAIT_UNCLOCKED); - cpu_do_idle(); - imx6q_set_lpm(WAIT_CLOCKED); - spin_unlock(&master_lock); - goto done; - } + spin_unlock(&cpuidle_lock);

-idle: cpu_do_idle(); -done: - atomic_dec(&master); + + spin_lock(&cpuidle_lock); + if (num_idle_cpus-- == num_online_cpus()) + imx6q_set_lpm(WAIT_CLOCKED); + spin_unlock(&cpuidle_lock);

return index; }