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

Peter Feuerer
2014-05-12T10:27:17Z

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@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.

thanks and kind regards,
--peter;