Message-ID: <20090524192219.GA30285@liondog.tnic>
Date:	Sun, 24 May 2009 21:22:19 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Peter Feuerer <peter@...e.net>
Cc:	LKML <linux-kernel@...r.kernel.org>, lenb@...nel.org,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Maxim Levitsky <maximlevitsky@...il.com>
Subject: Re: [PATCH] Acer Aspire One Fan Control

Hi,

On Mon, May 18, 2009 at 08:04:40PM +0200, Peter Feuerer wrote:
> Hi,
>
> sorry for the delay, was quite busy the last days. New patch attached. I 
> hope I didn't forget anything you suggested.
> As usual patched against and tested with current linus git.


> How does it work with those "Signed-off-by" and "Tested-by" lines,
>should I add you to the list of Signed-off people? Or is this done by
>the person who merges the patch?

There's an excellent manual explaining all that at length:
<Documentation/development-process/> and especially
<Documentation/development-process/5.Posting> and
<Documentation/SubmittingPatches, Section 14> which answers the
particular question you have. I could try to rephrase that here but
those documents explain it much better and extensively than I could.

> kind regards and many thanks for your help,
> --peter
>
>
>
> Signed-off-by: Peter Feuerer <peter@...e.net>

Ok, minor nitpicks below but it starting to shape up quite ok. You could
send it for inclusion upstream.

Reviewed-by: Borislav Petkov <petkovbb@...il.com>
Tested-by: Borislav Petkov <petkovbb@...il.com>

> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2b349ba..ded6b0c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -222,6 +222,13 @@ L:	linux-acenic@...site.dk
> S:	Maintained
> F:	drivers/net/acenic*
>
> +ACER ASPIRE ONE TEMPERATURE AND FAN DRIVER
> +P: Peter Feuerer
> +M: peter@...e.net
> +W: http://piie.net/?section=acerhdf
> +S: Maintained
> +F: drivers/platform/x86/acerhdf.c
> +
> ACER WMI LAPTOP EXTRAS
> P:	Carlos Corbacho
> M:	carlos@...angeworlds.co.uk
> diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
> index 284ebac..48b7362 100644
> --- a/drivers/platform/x86/Kconfig
> +++ b/drivers/platform/x86/Kconfig
> @@ -34,6 +34,23 @@ config ACER_WMI
> 	  If you have an ACPI-WMI compatible Acer/ Wistron laptop, say Y or M
> 	  here.
>
> +config ACERHDF
> +	tristate "Acer Aspire One temperature and fan driver"
> +	depends on THERMAL && THERMAL_HWMON
> +	---help---
> +	  This is a driver for Acer Aspire One netbooks. It allows to access
> +	  the temperature sensor and to control the fan.
> +
> +	  After loading this driver the BIOS controls still the fan.a

				    the BIOS is still in control of the fan

is better english, IMHO.

> +	  To let the kernel handle the fan, do:
> +	  echo -n enabled > /sys/class/thermal/thermal_zone0/mode
> +
> +	  For more information about this driver see
> +	  <http://piie.net/files/acerhdf_README.txt>
> +
> +	  If you have an Acer Aspire One netbook, say Y or M
> +	  here.
> +
> config ASUS_LAPTOP
> 	tristate "Asus Laptop Extras (EXPERIMENTAL)"
> 	depends on ACPI
> diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
> index e40c7bd..641b8bf 100644
> --- a/drivers/platform/x86/Makefile
> +++ b/drivers/platform/x86/Makefile
> @@ -9,6 +9,7 @@ obj-$(CONFIG_COMPAL_LAPTOP)	+= compal-laptop.o
> obj-$(CONFIG_DELL_LAPTOP)	+= dell-laptop.o
> obj-$(CONFIG_DELL_WMI)		+= dell-wmi.o
> obj-$(CONFIG_ACER_WMI)		+= acer-wmi.o
> +obj-$(CONFIG_ACERHDF)		+= acerhdf.o
> obj-$(CONFIG_HP_WMI)		+= hp-wmi.o
> obj-$(CONFIG_TC1100_WMI)	+= tc1100-wmi.o
> obj-$(CONFIG_SONY_LAPTOP)	+= sony-laptop.o
> diff --git a/drivers/platform/x86/acerhdf.c b/drivers/platform/x86/acerhdf.c
> new file mode 100644
> index 0000000..99ae2e6
> --- /dev/null
> +++ b/drivers/platform/x86/acerhdf.c
> @@ -0,0 +1,530 @@
> +/*
> + * acerhdf - A kernelmodule which monitors the temperature

s/kernelmodule/driver/

> + *           of the aspire one netbook, turns on/off the fan
> + *           as soon as the upper/lower threshold is reached.
> + *
> + * (C) 2009 - Peter Feuerer     peter (a) piie.net
> + *                              http://piie.net
> + *
> + * Inspired by and many thanks to:
> + *  o acerfand   - Rachel Greenham
> + *  o acer_ec.pl - Michael Kurz     michi.kurz (at) googlemail.com
> + *               - Petr Tomasek     tomasek (#) etf,cuni,cz
> + *               - Carlos Corbacho  cathectic (at) gmail.com
> + *               - Matthew Garrett
> + *               - Borislav Petkov
> + *
> + *  This program is free software; you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation; either version 2 of the License, or
> + *  (at your option) any later version.
> + *
> + *  This program is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with this program; if not, write to the Free Software
> + *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
> + */
> +
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/dmi.h>
> +#include <acpi/acpi_drivers.h>
> +#include <linux/sched.h>
> +#include <linux/thermal.h>
> +#include <linux/platform_device.h>
> +
> +/*
> + * if you want the module to be started in kernelmode,

s/kernelmode/kernel mode/g

> + * uncomment following line:
> + */
> +/* #define START_IN_KERNEL_MODE */

* define the following:
*/
#undef START_IN_KERNEL_MODE

is better

> +
> +#define VERSION "0.5.2"
> +
> +/*
> + * According to the Atom N270 datasheet,
> + * (http://download.intel.com/design/processor/datashts/320032.pdf) the
> + * CPU's optimal operating limits denoted in junction temperature as
> + * measured by the on-die thermal monitor are within 0 <= Tj <= 90. So,
> + * assume 89°C is critical temperature.
> + */
> +#define ACERHDF_TEMP_CRIT 89
> +#define ACERHDF_FAN_AUTO 1
> +#define ACERHDF_FAN_OFF 0
> +
> +/*
> + * No matter what value the user puts into the fanon variable, turn on the fan
> + * at 80 degree Celsius to prevent hardware damage
> + */
> +#define ACERHDF_MAX_FANON 80
> +
> +/*
> + * Maximal interval between to temperature checks is 20 seconds, as the die
> + * can get hot really fast under heavy load
> + */
> +#define ACERHDF_MAX_INTERVAL 20
> +
> +#define ACERHDF_ERROR -0xffff
> +
> +#define acerhdf_printk(loglevel, fmt, args...) \
> +	printk(loglevel "acerhdf: " fmt, ## args);
> +
> +#define acerhdf_notice(fmt, args...) \
> +	acerhdf_printk(KERN_NOTICE, fmt, ## args);
> +
> +#define acerhdf_error(fmt, args...) \
> +	acerhdf_printk(KERN_ERR, fmt, ## args);
> +
> +
> +#ifdef START_IN_KERNEL_MODE
> +static int kernelmode = 1;
> +#else
> +static int kernelmode;
> +#endif
> +
> +static int interval = 10;
> +static int fanon = 65;
> +static int fanoff = 60;
> +static int verbose;
> +static int fanstate = ACERHDF_FAN_AUTO;
> +static int disable_kernelmode;
> +static int bios_version = -1;
> +static char force_bios[16];
> +static int prev_interval;
> +struct thermal_zone_device *acerhdf_thz_dev;
> +struct thermal_cooling_device *acerhdf_cool_dev;

let's make all those module parameters unsigned just in case because you
can write negative values to them and acerhdf_check_param() won't catch
invalid values:

diff --git a/drivers/platform/x86/acerhdf.c b/drivers/platform/x86/acerhdf.c
index 99ae2e6..d4fc5d3 100644
--- a/drivers/platform/x86/acerhdf.c
+++ b/drivers/platform/x86/acerhdf.c
@@ -83,32 +83,32 @@
 
 
 #ifdef START_IN_KERNEL_MODE
-static int kernelmode = 1;
+static unsigned int kernelmode = 1;
 #else
-static int kernelmode;
+static unsigned int kernelmode;
 #endif
 
-static int interval = 10;
-static int fanon = 65;
-static int fanoff = 60;
-static int verbose;
-static int fanstate = ACERHDF_FAN_AUTO;
+static unsigned int interval = 10;
+static unsigned int fanon = 65;
+static unsigned int fanoff = 60;
+static unsigned int verbose;
+static unsigned int fanstate = ACERHDF_FAN_AUTO;
 static int disable_kernelmode;
 static int bios_version = -1;
 static char force_bios[16];
-static int prev_interval;
+static unsigned int prev_interval;
 struct thermal_zone_device *acerhdf_thz_dev;
 struct thermal_cooling_device *acerhdf_cool_dev;
 
-module_param(kernelmode, int, 0);
+module_param(kernelmode, uint, 0);
 MODULE_PARM_DESC(kernelmode, "Kernel mode on / off");
-module_param(interval, int, 0600);
+module_param(interval, uint, 0600);
 MODULE_PARM_DESC(interval, "Polling interval of temperature check");
-module_param(fanon, int, 0600);
+module_param(fanon, uint, 0600);
 MODULE_PARM_DESC(fanon, "Turn the fan on above this temperature");
-module_param(fanoff, int, 0600);
+module_param(fanoff, uint, 0600);
 MODULE_PARM_DESC(fanoff, "Turn the fan off below this temperature");
-module_param(verbose, int, 0600);
+module_param(verbose, uint, 0600);
 MODULE_PARM_DESC(verbose, "Enable verbose dmesg outputs");
 module_param_string(force_bios, force_bios, 16, 0);
 MODULE_PARM_DESC(force_bios, "Force BIOS version and omit BIOS check");

> +module_param(kernelmode, int, 0);
> +MODULE_PARM_DESC(kernelmode, "Kernel mode on / off");
> +module_param(interval, int, 0600);
> +MODULE_PARM_DESC(interval, "Polling interval of temperature check");
> +module_param(fanon, int, 0600);
> +MODULE_PARM_DESC(fanon, "Turn the fan on above this temperature");
> +module_param(fanoff, int, 0600);
> +MODULE_PARM_DESC(fanoff, "Turn the fan off below this temperature");
> +module_param(verbose, int, 0600);
> +MODULE_PARM_DESC(verbose, "Enable verbose dmesg outputs");

s/outputs/output/

> +module_param_string(force_bios, force_bios, 16, 0);
> +MODULE_PARM_DESC(force_bios, "Force BIOS version and omit BIOS check");
> +
> +/* BIOS settings */
> +struct bios_settings_t {
> +	const char *vendor;
> +	const char *version;
> +	unsigned char fanreg;
> +	unsigned char tempreg;
> +	unsigned char cmd_off;
> +	unsigned char cmd_auto;
> +};
> +
> +/* Register addresses and values for different BIOS versions */
> +static const struct bios_settings_t bios_settings[] = {
> +	{"Acer", "v0.3109", 0x55, 0x58, 0x1f, 0x00},
> +	{"Acer", "v0.3114", 0x55, 0x58, 0x1f, 0x00},
> +	{"Acer", "v0.3301", 0x55, 0x58, 0xaf, 0x00},
> +	{"Acer", "v0.3304", 0x55, 0x58, 0xaf, 0x00},
> +	{"Acer", "v0.3305", 0x55, 0x58, 0xaf, 0x00},
> +	{"Acer", "v0.3308", 0x55, 0x58, 0x21, 0x00},
> +	{"Acer", "v0.3309", 0x55, 0x58, 0x21, 0x00},
> +	{"Gateway", "v0.3103", 0x55, 0x58, 0x21, 0x00},
> +	{"Packard Bell", "v0.3105", 0x55, 0x58, 0x21, 0x00},
> +	{"", 0, 0, 0, 0, 0}
> +};
> +
> +
> +/* acer ec functions */
> +static int acerhdf_get_temp(void)
> +{
> +	u8 temp;
> +	/* read temperature */
> +	if (!ec_read(bios_settings[bios_version].tempreg, &temp)) {
> +		if (verbose)

you need to check the error status here before printing the temperature
since it might be invalid if the ec_read has failed:

	u8 temp;
	int err;

	err = ec_read(bios_settings[bios_version].tempreg, &temp);

	if (err)
		return ACERHDF_ERROR;

	if (verbose)
		acerhdf_notice("temp %d\n", temp);

	return temp;
}

> +			acerhdf_notice("temp %d\n", temp);
> +		return temp;
> +	}
> +	return ACERHDF_ERROR;
> +}
> +
> +static int acerhdf_get_fanstate(void)
> +{
> +	u8 fan;

need a new line here.

> +	if (!ec_read(bios_settings[bios_version].fanreg, &fan))
> +		return (fan == bios_settings[bios_version].cmd_off) ?
> +			ACERHDF_FAN_OFF : ACERHDF_FAN_AUTO;
> +
> +	return ACERHDF_ERROR;
> +}
> +
> +static void acerhdf_change_fanstate(int state)
> +{
> +	unsigned char cmd;
> +
> +	if (verbose)
> +		acerhdf_notice("fan %s\n", (state == ACERHDF_FAN_AUTO) ?
> +				"ON" : "OFF");
> +
> +	if (state == ACERHDF_FAN_AUTO) {
> +		cmd = bios_settings[bios_version].cmd_auto;
> +		fanstate = ACERHDF_FAN_AUTO;
> +	} else {
> +		cmd = bios_settings[bios_version].cmd_off;
> +		fanstate = ACERHDF_FAN_OFF;
> +	}
> +
> +	ec_write(bios_settings[bios_version].fanreg, cmd);
> +
> +}
> +
> +/* helpers */
> +static void acerhdf_check_param(struct thermal_zone_device *thermal)
> +{
> +	if (fanon > ACERHDF_MAX_FANON) {
> +		acerhdf_error("fanon temperature too high, set to %d\n",
> +				ACERHDF_MAX_FANON);
> +		fanon = ACERHDF_MAX_FANON;
> +	}
> +	if (kernelmode && prev_interval != interval) {
> +		if (interval > ACERHDF_MAX_INTERVAL) {
> +			acerhdf_error("interval too high, set to %d\n",
> +					ACERHDF_MAX_INTERVAL);
> +			interval = ACERHDF_MAX_INTERVAL;
> +		}
> +		if (verbose)
> +			acerhdf_notice("interval changed to: %d\n",
> +					interval);
> +		thermal->polling_delay = interval*1000;
> +		prev_interval = interval;
> +	}
> +}
> +
> +/* thermal zone callback functions */
> +static int acerhdf_get_ec_temp(struct thermal_zone_device *thermal,
> +		unsigned long *t)
> +{
> +	int temp;
> +
> +	acerhdf_check_param(thermal);
> +
> +	temp = acerhdf_get_temp();
> +	if (temp == ACERHDF_ERROR)
> +		return -EINVAL;
> +
> +	*t = temp;
> +	return 0;
> +}
> +
> +static int acerhdf_bind(struct thermal_zone_device *thermal,
> +		struct thermal_cooling_device *cdev)
> +{
> +	/* if the cooling device is the one from acerhdf bind it */
> +	if (cdev == acerhdf_cool_dev) {

you can save an indentation level here by exiting early:

	if (cdev != acerhdf_cool_dev)
		return 0;

	if (thermal_zone_bind_cooling_device(thermal, 0, cdev)) {
		acerhdf_error("error binding cooling dev\n");
		return -EINVAL;
	}

	return 0;
}

> +		if (thermal_zone_bind_cooling_device(thermal, 0, cdev)) {
> +			acerhdf_error("error binding cooling dev\n");
> +			return -EINVAL;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static int acerhdf_unbind(struct thermal_zone_device *thermal,
> +		struct thermal_cooling_device *cdev)
> +{
> +	if (cdev == acerhdf_cool_dev) {

same as above.

> +		if (thermal_zone_unbind_cooling_device(thermal, 0, cdev)) {
> +			acerhdf_error("acerhdf: error unbinding cooling dev\n");
> +			return -EINVAL;
> +		}
> +	}
> +	return 0;
> +}
> +
> +/*  current operation mode - enabled / disabled */
> +static int acerhdf_get_mode(struct thermal_zone_device *thermal,
> +		enum thermal_device_mode *mode)
> +{
> +	if (verbose)
> +		acerhdf_notice("kernelmode %d\n", kernelmode);

s/kernelmode/kernel mode/

> +
> +	*mode = (kernelmode) ? THERMAL_DEVICE_ENABLED :
> +		THERMAL_DEVICE_DISABLED;
> +
> +	return 0;
> +}
> +
> +/*
> + * set operation mode;
> + * enabled: the thermal layer of the kernel takes care about
> + *          the temperature and the fan.
> + * disabled: the BIOS takes control of the fan.
> + */
> +static int acerhdf_set_mode(struct thermal_zone_device *thermal,
> +		enum thermal_device_mode mode)
> +{
> +	if (mode == THERMAL_DEVICE_DISABLED) {
> +		acerhdf_notice("kernelmode OFF\n");

ditto.

> +		thermal->polling_delay = 0;
> +		thermal_zone_device_update(thermal);
> +		acerhdf_change_fanstate(ACERHDF_FAN_AUTO);
> +
> +		/*
> +		 * let the thermal layer disable kernelmode. This ensures that
> +		 * the thermal layer doesn't switch off the fan again
> +		 */
> +		disable_kernelmode = 1;
> +	} else {
> +		acerhdf_notice("kernelmode ON\n");

ditto.

> +		thermal->polling_delay = interval*1000;
> +		thermal_zone_device_update(thermal);
> +		kernelmode = 1;
> +	}
> +	return 0;
> +}
> +
> +static int acerhdf_get_trip_type(struct thermal_zone_device *thermal,
> +		int trip, enum thermal_trip_type *type)
> +{
> +	if (trip == 0)
> +		*type = THERMAL_TRIP_ACTIVE;
> +	return 0;
> +}
> +
> +static int acerhdf_get_trip_temp(struct thermal_zone_device *thermal,
> +		int trip, unsigned long *temp)
> +{
> +	if (trip == 0)
> +		*temp = fanon;
> +	return 0;
> +}
> +
> +static int acerhdf_get_crit_temp(struct thermal_zone_device *thermal,
> +		unsigned long *temperature)
> +{
> +	*temperature = ACERHDF_TEMP_CRIT;
> +	return 0;
> +}
> +
> +/* bind callback functions to thermalzone */
> +struct thermal_zone_device_ops acerhdf_device_ops = {
> +	.bind = acerhdf_bind,
> +	.unbind = acerhdf_unbind,
> +	.get_temp = acerhdf_get_ec_temp,
> +	.get_mode = acerhdf_get_mode,
> +	.set_mode = acerhdf_set_mode,
> +	.get_trip_type = acerhdf_get_trip_type,
> +	.get_trip_temp = acerhdf_get_trip_temp,
> +	.get_crit_temp = acerhdf_get_crit_temp,
> +};
> +
> +
> +/*
> + * cooling device callback functions
> + * get maximal fan cooling state
> + */
> +static int acerhdf_get_max_state(struct thermal_cooling_device *cdev,
> +		unsigned long *state)
> +{
> +	*state = 1;
> +	return 0;
> +}
> +
> +static int acerhdf_get_cur_state(struct thermal_cooling_device *cdev,
> +		unsigned long *state)
> +{
> +	unsigned long st = acerhdf_get_fanstate();
> +
> +	if (st == ACERHDF_ERROR)
> +		return -EINVAL;
> +
> +	*state = (st == ACERHDF_FAN_AUTO) ? 1 : 0;
> +	return 0;
> +}
> +
> +/* change current fan state - is overwritten when running in kernel mode */
> +static int acerhdf_set_cur_state(struct thermal_cooling_device *cdev,
> +		unsigned long state)
> +{
> +	int old_state;

well, this variable should be called current_state or similar but not
old since it is written through acerhdf_get_fanstate(), which returns
the current state.

> +
> +	/*
> +	 * let the thermal layer disable kernelmode. This ensures that
> +	 * the thermal layer doesn't switch off the fan again
> +	 */
> +	if (disable_kernelmode) {
> +		acerhdf_change_fanstate(ACERHDF_FAN_AUTO);
> +		disable_kernelmode = 0;
> +		kernelmode = 0;
> +		return 0;
> +	}
> +
> +	if (!kernelmode) {
> +		acerhdf_error("changing fan state is not allowed\n");
> +		return -EINVAL;
> +	}
> +
> +	old_state = acerhdf_get_fanstate();
> +
> +	/*
> +	 * if reading the fan's state returns unexpected value, there's a
> +	 * problem with the ec register. -> let the BIOS take control of
> +	 * the fan to prevent hardware damage
> +	 */
> +	if (old_state != fanstate) {
> +		acerhdf_error("failed reading fan state, "
> +				"disabling kernelmode.\n");

s/kernelmode/kernel mode/

> +
> +		if (verbose)
> +			acerhdf_error("read state: %d expected state: %d\n",
> +					old_state, fanstate);
> +
> +		acerhdf_change_fanstate(ACERHDF_FAN_AUTO);
> +		disable_kernelmode = 1;
> +	}
> +
> +	if (state == 0) {
> +		/* turn fan off only if below fanoff temperature */
> +		if ((old_state == ACERHDF_FAN_AUTO) &&
> +				(acerhdf_get_temp() < fanoff))

it might be cool to tell the user why you're not turning off the fan.

		if (verbose)
			acerhdf_notice("Not turning off fan due to current temp "
				       "exceeding fanoff value\n");

> +			acerhdf_change_fanstate(ACERHDF_FAN_OFF);
> +	} else {
> +		if (old_state == ACERHDF_FAN_OFF)
> +			acerhdf_change_fanstate(ACERHDF_FAN_AUTO);
> +	}
> +
> +	return 0;
> +}
> +
> +/* bind fan callbacks to fan device */
> +struct thermal_cooling_device_ops acerhdf_cooling_ops = {
> +	.get_max_state = acerhdf_get_max_state,
> +	.get_cur_state = acerhdf_get_cur_state,
> +	.set_cur_state = acerhdf_set_cur_state,
> +};
> +
> +/* check hardware */
> +static int acerhdf_check_hardware(void)
> +{
> +	int i;
> +	char const *vendor;
> +	char const *version;
> +	char const *release;
> +	char const *product;
> +
> +	/* get BIOS data */
> +	vendor  = dmi_get_system_info(DMI_SYS_VENDOR);
> +	version = dmi_get_system_info(DMI_BIOS_VERSION);
> +	release = dmi_get_system_info(DMI_BIOS_DATE);
> +	product = dmi_get_system_info(DMI_PRODUCT_NAME);
> +
> +
> +	acerhdf_notice("%s found BIOS vendor: \"%s\" version: \"%s\"\n",

let's split that line:

	acerhdf_notice("version %s\n", VERSION);
	acerhdf_notice("BIOS vendor: \"%s\", version: \"%s\"\n",
		       vendor, version);

> +	if (verbose)
> +		acerhdf_notice("BIOS release: \"%s\" product: \"%s\"\n",
> +				release, product);
> +
> +	if (!force_bios[0]) {
> +		/* check if product is a AO - Aspire One */
> +		if (strncmp(product, "AO", 2)) {
> +			acerhdf_error("no Aspire One hardware found\n");
> +			return ACERHDF_ERROR;
> +		}
> +	} else {
> +		acerhdf_notice("acerhdf: BIOS version: %s forced\n", version);
> +		version = force_bios;
> +		kernelmode = 0;
> +	}
> +
> +	/*
> +	 * if started with kernelmode off, prevent the kernel from switching
> +	 * off the fan
> +	 */
> +	if (!kernelmode) {
> +		disable_kernelmode = 1;
> +		acerhdf_notice("Fancontrol off, to enable:\n");

s/Fancontrol/Fan control/

> +		acerhdf_notice("echo -n \"enabled\" > "
> +			"/sys/class/thermal/thermal_zone0/mode\n");
> +		acerhdf_notice("http://piie.net/files/acerhdf_README.txt\n");
> +	}
> +
> +
> +	/* search BIOS version and BIOS vendor in BIOS settings table */
> +	for (i = 0; bios_settings[i].version[0]; ++i) {
> +		if (!strcmp(bios_settings[i].vendor, vendor) &&
> +				!strcmp(bios_settings[i].version, version)) {
> +			bios_version = i;
> +			break;
> +		}
> +	}
> +	if (bios_version == -1) {
> +		acerhdf_error("cannot find BIOS version\n");
> +		return ACERHDF_ERROR;
> +	}
> +	return 0;
> +}
> +
> +static int acerhdf_register_thermal(void)
> +{
> +	acerhdf_cool_dev = thermal_cooling_device_register("acerhdf-fan", NULL,
> +			&acerhdf_cooling_ops);
> +	if (IS_ERR(acerhdf_cool_dev))
> +		return ACERHDF_ERROR;
> +
> +	acerhdf_thz_dev = thermal_zone_device_register("acerhdf", 1,
> +			NULL, &acerhdf_device_ops, 0, 0, 0,
> +			(kernelmode) ? interval*1000 : 0);
> +	if (IS_ERR(acerhdf_thz_dev))
> +		return ACERHDF_ERROR;
> +
> +	return 0;
> +}
> +
> +static void acerhdf_unregister_thermal(void)
> +{
> +	if (acerhdf_cool_dev) {
> +		thermal_cooling_device_unregister(acerhdf_cool_dev);
> +		acerhdf_cool_dev = NULL;
> +	}
> +
> +	if (acerhdf_thz_dev) {
> +		thermal_zone_device_unregister(acerhdf_thz_dev);
> +		acerhdf_thz_dev = NULL;
> +	}
> +}
> +
> +/* kernel module init / exit functions */
> +static int __init acerhdf_init(void)
> +{
> +	if (acerhdf_check_hardware() == ACERHDF_ERROR)
> +		return -ENODEV;
> +
> +	if (acerhdf_register_thermal() == ACERHDF_ERROR) {
> +		acerhdf_unregister_thermal();
> +		return -ENODEV;
> +	}

let's make that function even one more readable:

static int __init acerhdf_init(void)
{

	if (acerhdf_check_hardware() == ACERHDF_ERROR)
		goto err;

	if (acerhdf_register_thermal() == ACERHDF_ERROR)
		goto err_unreg;

	return 0;

err_unreg:
	acerhdf_unregister_thermal();

err:
	return -EINVAL;
}

> +
> +	return 0;
> +}
> +
> +static void __exit acerhdf_exit(void)
> +{
> +	acerhdf_change_fanstate(ACERHDF_FAN_AUTO);
> +
> +	acerhdf_unregister_thermal();
> +}
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Peter Feuerer");
> +MODULE_DESCRIPTION("Aspire One temperature and fan driver");
> +MODULE_ALIAS("dmi:*:*Acer*:*:");
> +MODULE_ALIAS("dmi:*:*Gateway*:*:");
> +MODULE_ALIAS("dmi:*:*Packard Bell*:*:");
> +
> +/* what are the module init/exit functions */

no need for that comment

> +module_init(acerhdf_init);
> +module_exit(acerhdf_exit);

-- 
Regards/Gruss,
    Boris.
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