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

Javi Merino
2014-05-12T12:03:31Z

Hi Peter,

On Mon, May 12, 2014 at 11:27:08AM +0100, Peter Feuerer wrote:
> Javi Merino writes:
> > 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;
>
> 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.

Then for trip == 1 you should also write something in *temp if it's a
valid trip point and you don't want to return -EINVAL. I don't know
what is the correct hysteresis for trip == 1. Maybe 0? What I'm
trying to say is that you should return 0 only if you've updated
*temp.

Cheers,
Javi