Subject: [PATCH] drivers: cpuidle: don't initialize big.LITTLE driver if MCPM is unavailable

From: [email-masked] (Daniel Lezcano)
Date: Thu, 08 Jan 2015 09:53:47 +0100

On 01/08/2015 07:29 AM, Sudeep Holla wrote:
> If big.LITTLE driver is initialized even when MCPM is unavailable,
> we get the below warning the first time cpu tries to enter deeper
> C-states.

Can you elaborate why MCPM could be unavailable when the tc2 pm code 
registers the mcpm platform ops before the cpuidle driver ?

> ------------[ cut here ]------------
> WARNING: CPU: 4 PID: 0 at kernel/arch/arm/common/mcpm_entry.c:130 mcpm_cpu_suspend+0x6d/0x74()
> Modules linked in:
> CPU: 4 PID: 0 Comm: swapper/4 Not tainted 3.19.0-rc3-00007-gaf5a2cb1ad5c-dirty #11
> Hardware name: ARM-Versatile Express
> [<c0013fa5>] (unwind_backtrace) from [<c001084d>] (show_stack+0x11/0x14)
> [<c001084d>] (show_stack) from [<c04fe7f1>] (dump_stack+0x6d/0x78)
> [<c04fe7f1>] (dump_stack) from [<c0020645>] (warn_slowpath_common+0x69/0x90)
> [<c0020645>] (warn_slowpath_common) from [<c00206db>] (warn_slowpath_null+0x17/0x1c)
> [<c00206db>] (warn_slowpath_null) from [<c001cbdd>] (mcpm_cpu_suspend+0x6d/0x74)
> [<c001cbdd>] (mcpm_cpu_suspend) from [<c03c6919>] (bl_powerdown_finisher+0x21/0x24)
> [<c03c6919>] (bl_powerdown_finisher) from [<c001218d>] (cpu_suspend_abort+0x1/0x14)
> [<c001218d>] (cpu_suspend_abort) from [<00000000>] (  (null))
> ---[ end trace d098e3fd00000008 ]---
>
> This patch fixes the issue by checking for the availability of MCPM
> before initializing the big.LITTLE cpuidle driver
>
> Signed-off-by: Sudeep Holla <[email-masked]>
> Cc: Lorenzo Pieralisi <[email-masked]>
> Cc: Daniel Lezcano <[email-masked]>
> Cc: "Rafael J. Wysocki" <[email-masked]>
> ---
>   drivers/cpuidle/cpuidle-big_little.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/cpuidle/cpuidle-big_little.c b/drivers/cpuidle/cpuidle-big_little.c
> index e3e225fe6b45..40c34faffe59 100644
> --- a/drivers/cpuidle/cpuidle-big_little.c
> +++ b/drivers/cpuidle/cpuidle-big_little.c
> @@ -182,6 +182,10 @@ static int __init bl_idle_init(void)
>   	 */
>   	if (!of_match_node(compatible_machine_match, root))
>   		return -ENODEV;
> +
> +	if (!mcpm_is_available())
> +		return -EUNATCH;
> +
>   	/*
>   	 * For now the differentiation between little and big cores
>   	 * is based on the part number. A7 cores are considered little
>

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