linux-kernel - Re: [PATCH v3 4/6] acerhdf: Use bang-bang thermal governor

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Date:	Tue, 6 May 2014 11:50:29 +0100
From:	Javi Merino <javi.merino@....com>
To:	Peter Feuerer <peter@...e.net>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zhang Rui <rui.zhang@...el.com>, Andreas Mohr <andi@...as.de>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v3 4/6] acerhdf: Use bang-bang thermal governor

Hi Peter,

On Sat, May 03, 2014 at 06:59:24PM +0100, Peter Feuerer wrote:
> acerhdf has been doing an on-off fan control using hysteresis by
> post-manipulating the outcome of thermal subsystem trip point handling.
> This patch enables acerhdf to use the bang-bang governor, which is
> intended for on-off controlled fans.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> CC: Zhang Rui <rui.zhang@...el.com>
> Cc: Andreas Mohr <andi@...as.de>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Javi Merino <javi.merino@....com>
> Signed-off-by: Peter Feuerer <peter@...e.net>
> ---
>  drivers/platform/x86/Kconfig   |  2 +-
>  drivers/platform/x86/acerhdf.c | 34 +++++++++++++++++++++++++++++-----
>  2 files changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
> index 27df2c5..0c15d89 100644
> --- a/drivers/platform/x86/Kconfig
> +++ b/drivers/platform/x86/Kconfig
> @@ -38,7 +38,7 @@ config ACER_WMI
>  
>  config ACERHDF
>  	tristate "Acer Aspire One temperature and fan driver"
> -	depends on THERMAL && ACPI
> +	depends on ACPI && THERMAL_GOV_BANG_BANG
>  	---help---
>  	  This is a driver for Acer Aspire One netbooks. It allows to access
>  	  the temperature sensor and to control the fan.
> diff --git a/drivers/platform/x86/acerhdf.c b/drivers/platform/x86/acerhdf.c
> index 176edbd..afaa849 100644
> --- a/drivers/platform/x86/acerhdf.c
> +++ b/drivers/platform/x86/acerhdf.c
> @@ -50,7 +50,7 @@
>   */
>  #undef START_IN_KERNEL_MODE
>  
> -#define DRV_VER "0.5.30"
> +#define DRV_VER "0.5.31"
>  
>  /*
>   * According to the Atom N270 datasheet,
> @@ -259,6 +259,14 @@ static const struct bios_settings_t bios_tbl[] = {
>  
>  static const struct bios_settings_t *bios_cfg __read_mostly;
>  
> +/*
> + * this struct is used to instruct thermal layer to use bang_bang instead of
> + * default governor for acerhdf
> + */
> +static struct thermal_zone_params acerhdf_zone_params = {
> +	.governor_name = "bang_bang",
> +};
> +
>  static int acerhdf_get_temp(int *temp)
>  {
>  	u8 read_temp;
> @@ -440,6 +448,15 @@ static int acerhdf_get_trip_type(struct thermal_zone_device *thermal, int trip,
>  	return 0;
>  }
>  
> +static int acerhdf_get_trip_hyst(struct thermal_zone_device *thermal, int trip,
> +				 unsigned long *temp)
> +{
> +	if (trip == 0)
> +		*temp = fanon - fanoff;
> +
> +	return 0;
> +}
> +

I think you should only return 0 if you've updated the temperature.
Otherwise you're telling the calling function that everything went all
right but you may be leaving garbage in *temp.  What about

	if (trip != 0)
		return -EINVAL;

	*temp = fanon - fanoff;
	return 0;

Cheers,
Javi

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