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

[Peter Feuerer]

Hi Javi,

Javi Merino writes:

> 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@xxxxxxxxxxxxxxxxxxxx>
> > CC: Zhang Rui <rui.zhang@xxxxxxxxx>
> > Cc: Andreas Mohr <andi@xxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxx>
> > Cc: Javi Merino <javi.merino@xxxxxxx>
> > Signed-off-by: Peter Feuerer <peter@xxxxxxxx>
> > ---
> >  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;

Yes, sounds good.  What about trip == 1?  This is a valid trip point for 
acerhdf (critical) and one could argue, that it has a valid hysteresis of 
0.  - Thus EINVAL would be wrong here.

thanks and kind regards,
--peter;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/