Re: [PATCH] sh: fix cpuidle on sh7724, possibly others

[Paul Mundt <lethal@linux-sh.org>]

On Wed, Dec 07, 2011 at 09:38:13AM +0100, Guennadi Liakhovetski wrote:
> cpuidle has been broken on sh7724 and, possibly, other SuperH SoCs since 
> 
> commit f533c3d340536198a4889a42a68d6c0d79a504e7
> Author: Paul Mundt <lethal@linux-sh.org>
> Date:   Fri Oct 16 17:20:58 2009 +0900
> 
>     sh: Idle loop chainsawing for SMP-based light sleep.
> 
> i.e., since 2.6.33-rc1. The reason is a missing local_irq_enable() on the 
> path, actually entering a sleep mode. This patch adds the missing call.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
> 
> This fixes one of the problem with cpuidle on sh. When applied (suitably 
> adjusted) directly after f533c3d340536198a4889a42a68d6c0d79a504e7, it does 
> fix the problem. However, since that commit cpuidle has been broken (at 
> least for my configuration) at least once more. This time bisection points 
> out at
> 
> commit 03625e7107cde46e2851557ec06426799e6ae7f2
> Author: Magnus Damm <damm@opensource.se>
> Date:   Fri Oct 30 04:24:32 2009 +0000
> 
>     sh: Use RSMEM for sleep code on sh7724
> 
> Still investigating.
> 
> diff --git a/arch/sh/kernel/cpu/shmobile/cpuidle.c b/arch/sh/kernel/cpu/shmobile/cpuidle.c
> index 1cc257c..e58640a 100644
> --- a/arch/sh/kernel/cpu/shmobile/cpuidle.c
> +++ b/arch/sh/kernel/cpu/shmobile/cpuidle.c
> @@ -48,6 +48,7 @@ static int cpuidle_sleep_enter(struct cpuidle_device *dev,
>  	 */
>  	k = min_t(int, allowed_state, requested_state);
>  
> +	local_irq_enable();
>  	before = ktime_get();
>  	sh_mobile_call_standby(cpuidle_mode[k]);
>  	after = ktime_get();

Thanks for debugging this. This looks like a simple imbalance to me, but
the changeset you cite doesn't do any SR toggling that would account for
it, so that makes me suspect something else.

Looking at the code in question, perhaps this is the culprit?

---

diff --git a/arch/sh/kernel/cpu/shmobile/pm.c b/arch/sh/kernel/cpu/shmobile/pm.c
index a6f95ae..55b9024 100644
--- a/arch/sh/kernel/cpu/shmobile/pm.c
+++ b/arch/sh/kernel/cpu/shmobile/pm.c
@@ -136,7 +136,7 @@ static int sh_pm_enter(suspend_state_t state)
 	local_irq_disable();
 	set_bl_bit();
 	sh_mobile_call_standby(SUSP_MODE_STANDBY_SF);
-	local_irq_disable();
+	local_irq_enable();
 	clear_bl_bit();
 	return 0;
 }