[PATCH] ARM: EXYNOS: Fix coupled CPU idle freeze on Exynos4210

[Marc Zyngier]

On 21/03/18 09:45, Marek Szyprowski wrote:
> Since commit 04c8b0f82c7d ("irqchip/gic: Make locking a BL_SWITCHER only
> feature") coupled CPU idle freezes from time to time on Exynos4210. Later
> commit 313c8c16ee62 ("PM / CPU: replace raw_notifier with atomic_notifier")
> changed the context in which the CPU idle code is executed, what results
> in fully reproducible freeze all the time. However, almost the same coupled
> CPU idle code works fine on Exynos3250 regarless of the changes made in
> the mentioned commits.
> 
> It turned out that the IPI call used on Exynos4210 is conflicting with the
> change done in the first mentioned commit in GIC. Fix this by using the
> same code path as for Exynos3250, instead of the IPI call for
> synchronization with second CPU core, call dsb_sev() directly.
> 
> Tested on Exynos4210-based Trats and Origen boards.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> CC: stable at vger.kernel.org # v4.13+
> ---
>  arch/arm/mach-exynos/pm.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/arm/mach-exynos/pm.c b/arch/arm/mach-exynos/pm.c
> index dc4346ecf16d..a1055a2b8d54 100644
> --- a/arch/arm/mach-exynos/pm.c
> +++ b/arch/arm/mach-exynos/pm.c
> @@ -271,11 +271,7 @@ static int exynos_cpu0_enter_aftr(void)
>  				goto fail;
>  
>  			call_firmware_op(cpu_boot, 1);
> -
> -			if (soc_is_exynos3250())
> -				dsb_sev();
> -			else
> -				arch_send_wakeup_ipi_mask(cpumask_of(1));
> +			dsb_sev();
>  		}
>  	}
>  fail:
> 

I'm a bit puzzled here.

If the GIC change broke something on your platform, it probably also
broke something for all other users of arch_send_wakeup_ipi_mask. But
nobody reported anything until now. Also, it doesn't look like 4210 is a
big-little platform, so it is unlikely to use the big-little switcher.

What is specific to this system that makes misbehave? Were you
implicitly relying on the BL lock to perform some serialization?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...