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

Javi Merino
2014-05-06T10:50:38Z

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@linux-foundation.org>
> CC: Zhang Rui <rui.zhang@intel.com>
> Cc: Andreas Mohr <andi@lisas.de>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Javi Merino <javi.merino@arm.com>
> Signed-off-by: Peter Feuerer <peter@piie.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