linux-kernel - Re: [PATCH 3.14 52/64] thermal: step

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Date:	Fri, 12 Jun 2015 12:58:23 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>,
	Jean Delvare <jdelvare@...e.de>,
	Peter Feuerer <peter@...e.net>,
	Kamal Mostafa <kamal@...onical.com>
Subject: Re: [PATCH 3.14 52/64] thermal: step_wise: Revert optimization

On Wed, Jun 03, 2015 at 08:43:20PM +0900, Greg Kroah-Hartman wrote:
> 3.14-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Jean Delvare <jdelvare@...e.de>
> 
> Commit 178c2490b99f898efc06d1ad75cadc84f13021a6 ("thermal: step_wise:
> cdev only needs update on a new target state") broke driver acerhdf.
> That driver abused the step_wise thermal governor until the bang_bang
> governor was available, and the optimization broke this usage model.
> 
> Kernels v3.12 to v3.18 are affected. In v3.19 the acerhdf driver was
> switched to the bang_bang governor and that solved the problem.
> 
> For kernels v3.12 to v3.17, the bang_bang governor isn't available
> yet so the easiest fix is to revert the optimization.
> 
> Signed-off-by: Jean Delvare <jdelvare@...e.de>
> Reported-by: Dieter Jurzitza (https://bugzilla.opensuse.org/show_bug.cgi?id=925961)
> Tested-by: Peter Feuerer <peter@...e.net>
> Tested-by: Dieter Jurzitza
> ---
> Please consider this patch for stable kernel branches from v3.12 to v3.17.
> 
> If anyone cares about v3.18, I think a better fix would be to backport
> commit 48c8dd64345ba2a8c41556095c7adacb1c8af7c1 ("acerhdf: Use bang-bang
> thermal governor") but it's too big for stable, so it's left to
> distributions. So maybe this fix should make it into v3.18 stable as
> well - I'll let whoever maintains that branch decide.
>

Thanks, I am also queuing this patch for the 3.16 kernel.  And I guess
3.13 could also pick it (Cc'ing Kamal).

Cheers,
--
Luís

>  drivers/thermal/step_wise.c |    3 ---
>  1 file changed, 3 deletions(-)
> 
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -146,9 +146,6 @@ static void thermal_zone_trip_update(str
>  		dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
>  					old_target, (int)instance->target);
>  
> -		if (old_target == instance->target)
> -			continue;
> -
>  		/* Activate a passive thermal instance */
>  		if (old_target == THERMAL_NO_TARGET &&
>  			instance->target != THERMAL_NO_TARGET)
> 
> 
> --
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