Date:	Thu, 06 Aug 2009 09:08:39 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Zhang Rui <rui.zhang@...el.com>
Cc:	linux-acpi <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	Len Brown <lenb@...nel.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>
Subject: Re: [RFC PATCH V2 1/2] introduce ALS sysfs class

On Thu, 2009-08-06 at 16:31 +0800, Zhang Rui wrote:
> Introduce ALS sysfs class device.
> 
> ALS sysfs class device provides a standard sysfs interface
> for Ambient Light Sensor devices.
> 
> Only two sysfs I/F are introduced currently.
> /sys/class/als/alsX/illuminance:
> 	indicates the amount of light incident upon a specified surface area.
> /sys/class/als/alsX/mappings:
> 	exports ambient light illuminance to display luminance mappings
> 	that can be used by an OS to calibrate its ambient light policy
> 	for a given sensor configuration.
> 	The OS can use this information to extrapolate an ALS response curve
> 	- noting that these values may be treated differently depending on the
> 	OS implementation but should be used in some form to calibrate ALS policy.
> 
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> ---
>  Documentation/als/sysfs.txt |  138 ++++++++++++++++++++++
>  drivers/Kconfig             |    2 
>  drivers/Makefile            |    1 
>  drivers/als/Kconfig         |   10 +
>  drivers/als/Makefile        |    5 
>  drivers/als/als_sys.c       |  269 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/als_sys.h     |   57 +++++++++
>  7 files changed, 482 insertions(+)
> 
> Index: linux-2.6/drivers/Kconfig
> ===================================================================
> --- linux-2.6.orig/drivers/Kconfig
> +++ linux-2.6/drivers/Kconfig
> @@ -62,6 +62,8 @@ source "drivers/power/Kconfig"
>  
>  source "drivers/hwmon/Kconfig"
>  
> +source "drivers/als/Kconfig"
> +
>  source "drivers/thermal/Kconfig"
>  
>  source "drivers/watchdog/Kconfig"
> Index: linux-2.6/drivers/Makefile
> ===================================================================
> --- linux-2.6.orig/drivers/Makefile
> +++ linux-2.6/drivers/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_PPS)		+= pps/
>  obj-$(CONFIG_W1)		+= w1/
>  obj-$(CONFIG_POWER_SUPPLY)	+= power/
>  obj-$(CONFIG_HWMON)		+= hwmon/
> +obj-$(CONFIG_ALS)		+= als/
>  obj-$(CONFIG_THERMAL)		+= thermal/
>  obj-$(CONFIG_WATCHDOG)		+= watchdog/
>  obj-$(CONFIG_PHONE)		+= telephony/
> Index: linux-2.6/drivers/als/Kconfig
> ===================================================================
> --- /dev/null
> +++ linux-2.6/drivers/als/Kconfig
> @@ -0,0 +1,10 @@
> +#
> +# Ambient Light Sensor sysfs device configuration
> +#
> +
> +menuconfig ALS
> +	tristate "Ambient Light Sensor sysfs device"
> +	help
> +	  This framework provides a generic sysfs I/F for Ambient Light

"interface", not "I/F"

> +	  Sensor devices.
> +	  If you want this support, you should say Y or M here.
> Index: linux-2.6/drivers/als/Makefile
> ===================================================================
> --- /dev/null
> +++ linux-2.6/drivers/als/Makefile
> @@ -0,0 +1,5 @@
> +#
> +# Makefile for sensor chip drivers.
> +#
> +
> +obj-$(CONFIG_ALS)		+= als_sys.o
> Index: linux-2.6/drivers/als/als_sys.c
> ===================================================================
> --- /dev/null
> +++ linux-2.6/drivers/als/als_sys.c
> @@ -0,0 +1,269 @@
> +/*
> + *  als_sys.c - Ambient Light Sensor Sysfs support.
> + *
> + *  Copyright (C) 2009 Intel Corp
> + *  Copyright (C) 2009 Zhang Rui <rui.zhang@...el.com>
> + *
> + *  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + *
> + *  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; version 2 of the License.
> + *
> + *  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/module.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/als_sys.h>
> +
> +MODULE_AUTHOR("Zhang Rui");
> +MODULE_DESCRIPTION("Ambient Light Sensor sysfs support");
> +MODULE_LICENSE("GPL");
> +
> +#define PREFIX "ALS: "
> +
> +struct als_mapping_item {
> +	struct kobject kobj;
> +	int index;
> +	struct list_head node;
> +};
> +
> +/* sys I/F for Ambient Light Sensor */
> +
> +#define to_als_device(dev) container_of(dev, struct als_device, device)
> +
> +static ssize_t
> +desc_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	struct als_device *als = to_als_device(dev);
> +
> +	return sprintf(buf, "%s\n", als->desc ? als->desc : "N/A");
> +}
> +
> +static ssize_t
> +illuminance_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	struct als_device *als = to_als_device(dev);
> +	int illuminance;
> +	int result;
> +
> +	result = als->ops->get_illuminance(als, &illuminance);
> +	if (result)
> +		return result;
> +
> +	if (!illuminance)
> +		return sprintf(buf, "Illuminance below the supported range\n");
> +	else if (illuminance == -1)
> +		return sprintf(buf, "Illuminance above the supported range\n");
> +	else if (illuminance < -1)
> +		return -ERANGE;
> +	else
> +		return sprintf(buf, "%d\n", illuminance);
> +}
> +
> +static DEVICE_ATTR(desc, 0444, desc_show, NULL);
> +static DEVICE_ATTR(illuminance, 0444, illuminance_show, NULL);
> +
> +#define ATTR(_name, _mode)	\
> +	struct attribute als_##_name##_attr = {	\
> +		.name = __stringify(_name),	\
> +		.mode = _mode,			\
> +	};
> +
> +static ATTR(illuminance, 0444);
> +static ATTR(adjustment, 0444);
> +
> +static struct attribute * als_mapping_attrs[] = {
> +	&als_illuminance_attr,
> +	&als_adjustment_attr,
> +	NULL,
> +};
> +
> +static ssize_t show_mapping_info(struct kobject *kobj,
> +				       struct attribute *attr, char *buf)
> +{
> +	struct device *dev = container_of(kobj->parent, struct device, kobj);
> +	struct als_device *als = to_als_device(dev);
> +	int index, illuminance, adjustment;
> +	int result;
> +
> +	if (!sscanf(kobj->name, "mapping%d", &index))
> +		return -EINVAL;
> +
> +	result = als->ops->get_mapping_info(als, index, &illuminance, &adjustment);
> +	if (result)
> +		return result;
> +
> +	return sprintf(buf, "%u\n", (attr == &als_illuminance_attr) ? illuminance : adjustment);
> +}
> +
> +static struct sysfs_ops als_mapping_info_ops = {
> +	.show = show_mapping_info,
> +	.store = NULL,
> +};
> +
> +static struct kobj_type als_mapping_ktype = {
> +	.sysfs_ops = &als_mapping_info_ops,
> +	.default_attrs = als_mapping_attrs,
> +};
> +
> +static void als_release(struct device *dev) {

Open brace on next line.

> +	struct als_device *als = to_als_device(dev);
> +
> +	if (als->desc)
> +		kfree(als->desc);
> +	kfree(als);
> +}
> +
> +static struct class als_class = {
> +	.name = "als",
> +	.dev_release = als_release,
> +};
> +
> +/**
> + * als_device_update_mappings - update the ambient light illuminance to
> + * 				display luminance adjustment mappings
> + */
> +int als_device_update_mappings(struct als_device *als)
> +{
> +	int old_count = als->count;
> +	int i;
> +	struct als_mapping_item *pos, *next;
> +	int result;
> +
> +	result = als->ops->get_mapping_count(als, &als->count);
> +	if (result)
> +		return result;
> +
> +	if (old_count == als->count)
> +		return 0;
> +
> +	if (als->count > old_count)
> +		for (i = old_count; i < als->count; i++) {
> +			pos = kzalloc(sizeof(struct als_mapping_item), GFP_KERNEL);
> +			if (!pos)
> +				return -ENOMEM;
> +
> +			pos->index = i;
> +			result = kobject_init_and_add(&pos->kobj, &als_mapping_ktype,
> +					&als->device.kobj, "mapping%d", pos->index);
> +			if (result)
> +				break;
> +		}
> +	else
> +		list_for_each_entry_safe(pos, next, &als->mappings, node) {
> +			if (pos->index < als->count)
> +				continue;
> +			list_del(&pos->node);
> +			kobject_put(&pos->kobj);
> +			kfree(pos);
> +		}
> +
> +	if (result)
> +		als->count = i;
> +
> +	return 0;
> +}
> +
> +EXPORT_SYMBOL(als_device_update_mappings);
> +
> +/**
> + * als_device_register - register a new Ambient Light Sensor class device
> + * @ops:	standard ALS devices callbacks.
> + * @devdata:	device private data.
> + */
> +struct als_device *als_device_register(struct als_device_ops *ops,
> +				       char *desc, void *devdata)
> +{
> +	struct als_device *als;
> +	static int als_id;
> +	int result;
> +
> +	if (!ops || !ops->get_illuminance)
> +		return ERR_PTR(-EINVAL);

I probably wouldn't bother with these null pointer checks.
Your ACPI ALS driver does check for failure, but others may
not.  If a broken driver supplies a null pointer here, we'll
oops pretty fast, and the backtrace will show exactly what
the problem is.

> +
> +	als = kzalloc(sizeof(struct als_device), GFP_KERNEL);
> +	if (!als)
> +		return ERR_PTR(-ENOMEM);
> +
> +	als->ops = ops;
> +	als->device.class = &als_class;
> +	als->devdata = devdata;
> +	als->id = als_id++;
> +	INIT_LIST_HEAD(&als->mappings);
> +	if (desc) {
> +		als->desc = kzalloc(strlen(desc), GFP_KERNEL);
> +		if (!als->desc) {
> +			kfree(als);
> +			return ERR_PTR(-ENOMEM);
> +		}
> +		strcpy(als->desc, desc);
> +	}
> +	dev_set_name(&als->device, "als%d", als->id);
> +	result = device_register(&als->device);
> +	if (result) {
> +		if (als->desc)
> +			kfree(als->desc);
> +		kfree(als);
> +		return ERR_PTR(result);
> +	}
> +
> +	/* sys I/F */
> +	result = device_create_file(&als->device, &dev_attr_illuminance);
> +	if (result)
> +		goto unregister_device;
> +
> +	result = device_create_file(&als->device, &dev_attr_desc);
> +	if (result)
> +		goto unregister_device;
> +
> +	return als;
> +
> +unregister_device:
> +	device_unregister(&als->device);
> +	return ERR_PTR(result);
> +}
> +
> +EXPORT_SYMBOL(als_device_register);
> +
> +/**
> + * als_device_unregister - removes the registered ALS device
> + * @als:	the ALS device to remove.
> + */
> +void als_device_unregister(struct als_device *als)
> +{
> +	if (!als)
> +		return;

Unnecessary null pointer check.

> +
> +	device_remove_file(&als->device, &dev_attr_desc);
> +	device_remove_file(&als->device, &dev_attr_illuminance);
> +
> +	device_unregister(&als->device);
> +	return;
> +}
> +
> +EXPORT_SYMBOL(als_device_unregister);
> +
> +static int __init als_init(void)
> +{
> +	return class_register(&als_class);
> +}
> +
> +static void __exit als_exit(void)
> +{
> +	class_unregister(&als_class);
> +}
> +
> +subsys_initcall(als_init);
> +module_exit(als_exit);
> Index: linux-2.6/include/linux/als_sys.h
> ===================================================================
> --- /dev/null
> +++ linux-2.6/include/linux/als_sys.h
> @@ -0,0 +1,57 @@
> +/*
> + *  als.h  ($Revision: 0 $)
> + *
> + *  Copyright (C) 2009  Intel Corp
> + *  Copyright (C) 2009  Zhang Rui <rui.zhang@...el.com>
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + *  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; version 2 of the License.
> + *
> + *  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.
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + */
> +
> +#ifndef __ALS_SYS_H__
> +#define __ALS_SYS_H__
> +
> +#include <linux/device.h>
> +
> +struct als_device;
> +
> +struct als_device_ops {
> +	int (*get_illuminance) (struct als_device *, int *);
> +	int (*get_mapping_count) (struct als_device *, int *);
> +	int (*get_mapping_info) (struct als_device *, int, int *, int *);
> +};
> +
> +struct als_mapping {
> +	int illuminance;
> +	int adjustment;
> +};
> +
> +struct als_device {
> +	int id;
> +	int illuminance;
> +	struct device device;
> +	struct als_device_ops *ops;
> +	void *devdata;
> +	char *desc;
> +	int count;
> +	struct list_head mappings;
> +};
> +
> +int als_device_update_mappings(struct als_device *als);
> +struct als_device *als_device_register(struct als_device_ops *, char *, void *);
> +void als_device_unregister(struct als_device *);
> +
> +#endif /* __ALS_SYS_H__ */
> Index: linux-2.6/Documentation/als/sysfs.txt
> ===================================================================
> --- /dev/null
> +++ linux-2.6/Documentation/als/sysfs.txt
> @@ -0,0 +1,138 @@
> +Ambient Light Sensor Sysfs driver How To
> +=========================
> +
> +Written by Zhang Rui <rui.zhang@...el.com>
> +
> +Updated: 6 August 2009
> +
> +Copyright (c)  2009 Intel Corporation
> +
> +0. Introduction
> +
> +The generic Ambient Light Sensor sysfs provides a standard interface for ALS devices.
> +
> +User space can use this interface to get the status of the ambient light environment
> +the system is currently in, and get the ambient light illuminance to display luminance
> +mappings to calibrate its ambient light policy for a given sensor configuration.
> +
> +An intelligent ALS application can make ambient light decisions based on inputs
> +from these ALS attributes and adjust the LVDS brightness levels.
> +
> +[0-*]	denotes any positive number starting from 0

You might use just "N" instead of "[0-*]", i.e.,
"/sys/class/als/alsN" is a common informal shorthand for
"als0, als1, als2, etc".

> +
> +Two acronyms that used in this HOW TO only:
> +ALI	ambient light illuminace
> +DLA	display luminance adjustment (or display brightness adjustment)
> +
> +1. Ambient Light Sensor sysfs driver interface functions
> +
> +1.1 struct als_device *als_device_register(struct als_device_ops *ops, char *desc, void *devdata)
> +
> +	This interface function adds a new ALS device to
> +	/sys/class/als folder as als[0-*].
> +
> +	ops:	thermal zone device call-backs.
> +		.get_illuminance: get the current ALI.
> +		.get_mappings_count: get the number of ALI to DLA mappings.
> +		.get_mapping_info: get the info of a specified ALI to DLA mapping.
> +	desc:	a description of the ALS device.
> +	devdata:device private data
> +
> +1.2 void als_device_unregister(struct als_device *als)
> +
> +	This interface function removes the ALS device.
> +	It deletes the corresponding entry form /sys/class/als folder.
> +
> +1.3 int als_device_update_mappings(struct als_device *als)
> +
> +	This interface updates the ALI to DLA mappings.
> +	This is usually invoked by the native ALS driver when it detects a mapping change.
> +
> +2. sysfs attributes structure
> +
> +RO	read only value
> +RW	read/write value
> +
> +ALS sysfs attributes will be represented under /sys/class/als.
> +
> +/sys/class/als/als[0-*]:
> +	|-----desc:			Strings which describes the ALS device
> +	|-----illuminance:		Current ALI
> +	|-----mapping[0-*]:
> +		|-----illuminance:	ALI threshold when an DLA is needed
> +		|-----adjustment:	how to do the DLA when the threshold is hit
> +
> +***********************************
> +* Ambient Light Sendor attributes *
> +***********************************
> +
> +desc				Strings which descibes the current ALS.
> +				This is given by native ALS driver as part of registration.
> +				Eg: ACPI ALS driver gives the full pathname of
> +				the ALS device in ACPI namespace.
> +				RO
> +				Required
> +
> +illuminance			Current ALI reported by native ALS driver
> +				Unit: lux (lumens per square meter)
> +				RO
> +				Required
> +
> +mapping[0-*]			represent one item of the ALI to DLA mappings.
> +
> +mapping[0-*]/illuminance	ALI threshold when an DLA is needed
> +				RO
> +
> +mapping[0-*]/adjustment		a relative percentages in order simplify the means
> +				by which these adjustments are applied in lieu of
> +				changes to the user’s display brightness preference.
> +				A value of 100 is used to indicate no (0%) display
> +				brightness adjustment.
> +				Values less than 100 indicate a negative adjustment
> +				(dimming); values greater than 100 indicate a positive
> +				adjustment (brightening).
> +				RO
> +
> +3. How to implement ALS control in user space
> +
> +To implement the ALS control, including both ALI detection and Backlight
> +adjustment, interactions between backlight driver and als driver are needed.
> +It's ugly to implement such a driver in Linux kenrel.

s/kenrel/kernel/

> +A user space application is preferred in this case.
> +
> +Below is a simple example about how to do ALS mangement in user space.

s/about/of/
s/mangement/management/

> +
> +This is the ACPI backlight sysfs I/F
> +/sys/class/backlight/acpi_video0:
> +	|-----brightness	6
> +	|-----actual_brightness	6
> +	|-----max_brightness	10
> +
> +And this is the ACPI ALS sysfs I/F
> +/sys/class/als/als0:
> +	|-----illuminance		500
> +	|-----mapping[0]
> +		|-----illuminance	0
> +		|-----adjustment	50
> +	|-----mapping[1]
> +		|-----illuminance	200
> +		|-----adjustment	70
> +	|-----mapping[2]
> +		|-----illuminance	600
> +		|-----adjustment	100
> +	|-----mapping[3]
> +		|-----illuminance	900
> +		|-----adjustment	125
> +	|-----mapping[4]
> +		|-----illuminance	1200
> +		|-----adjustment	150
> +
> +If user thinks that brightness level 6 is good enough for him when ALI is 600,
> +he can set brightness 6 as the user’s display brightness preference.
> +When user goes to the base-room with the laptop and the ALI changes to 200,

s/base-room/basement/

> +the ALS application knows that it should do a -25% display brightness
> +adjustment, i.e. changes the backlight to 4.
> +And when the laptop is used outdoors, where the ALI reaches 1200,
> +the ALS application should do a +50% adjustment,
> +i.e. run "echo 9 > /sys/class/backlight/acpi_video0/brightness".
> +
> 
> 

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