Date:	Fri, 20 Apr 2012 17:00:48 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	MyungJoo Ham <myungjoo.ham@...sung.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hjønnevag <arve@...roid.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Morten CHRISTIANSEN <morten.christiansen@...ricsson.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	John Stultz <john.stultz@...aro.org>, myungjoo.ham@...il.com,
	cw00.choi@...sung.com
Subject: Re: [PATCH v8 resend 1/6] Extcon (external connector): import Android's
 switch class and modify.

On 20/04/12 15:16, MyungJoo Ham wrote:
> External connector class (extcon) is based on and an extension of
> Android kernel's switch class located at linux/drivers/switch/.
>
> This patch provides the before-extension switch class moved to the
> location where the extcon will be located (linux/drivers/extcon/) and
> updates to handle class properly.
>
> The before-extension class, switch class of Android kernel, commits
> imported are:
>
> switch: switch class and GPIO drivers. (splitted)
> Author: Mike Lockwood <lockwood@...roid.com>
>
> switch: Use device_create instead of device_create_drvdata.
> Author: Arve Hjønnevåg <arve@...roid.com>
>
> In this patch, upon the commits of Android kernel, we have added:
> - Relocated and renamed for extcon.
> - Comments, module name, and author information are updated
> - Code clean for successing patches
> - Bugfix: enabling write access without write functions
> - Class/device/sysfs create/remove handling
> - Added comments about uevents
> - Format changes for extcon_dev_register() to have a parent dev.
>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
> Reviewed-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>

Hi Myungjoo,

A few comments below.

~Ryan

> --
> Changes from v7
> - Compiler error fixed when it is compiled as a module.
> - Removed out-of-date Kconfig entry
>
> Changes from v6
> - Updated comment/strings
> - Revised "Android-compatible" mode.
>    * Automatically activated if CONFIG_ANDROID && !CONFIG_ANDROID_SWITCH
>    * Creates /sys/class/switch/*, which is a copy of /sys/class/extcon/*
>
> Changes from v5
> - Split the patch
> - Style fixes
> - "Android-compatible" mode is enabled by Kconfig option.
>
> Changes from v2
> - Updated name_show
> - Sysfs entries are handled by class itself.
> - Updated the method to add/remove devices for the class
> - Comments on uevent send
> - Able to become a module
> - Compatible with Android platform
>
> Changes from RFC
> - Renamed to extcon (external connector) from multistate switch
> - Added a seperated directory (drivers/extcon)
> - Added kerneldoc comments
> - Removed unused variables from extcon_gpio.c
> - Added ABI Documentation.
> ---
>  Documentation/ABI/testing/sysfs-class-extcon |   26 +++
>  drivers/Kconfig                              |    2 +
>  drivers/Makefile                             |    1 +
>  drivers/extcon/Kconfig                       |   17 ++
>  drivers/extcon/Makefile                      |    5 +
>  drivers/extcon/extcon_class.c                |  236 ++++++++++++++++++++++++++
>  include/linux/extcon.h                       |   82 +++++++++
>  7 files changed, 369 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-extcon
>  create mode 100644 drivers/extcon/Kconfig
>  create mode 100644 drivers/extcon/Makefile
>  create mode 100644 drivers/extcon/extcon_class.c
>  create mode 100644 include/linux/extcon.h
>
> diff --git a/Documentation/ABI/testing/sysfs-class-extcon b/Documentation/ABI/testing/sysfs-class-extcon
> new file mode 100644
> index 0000000..59a4b1c
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-extcon
> @@ -0,0 +1,26 @@
> +What:		/sys/class/extcon/.../
> +Date:		December 2011
> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
> +Description:
> +		Provide a place in sysfs for the extcon objects.
> +		This allows accessing extcon specific variables.
> +		The name of extcon object denoted as ... is the name given
> +		with extcon_dev_register.
> +
> +What:		/sys/class/extcon/.../name
> +Date:		December 2011
> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
> +Description:
> +		The /sys/class/extcon/.../name shows the name of the extcon
> +		object. If the extcon object has an optional callback
> +		"show_name" defined, the callback will provide the name with
> +		this sysfs node.
> +
> +What:		/sys/class/extcon/.../state
> +Date:		December 2011
> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
> +Description:
> +		The /sys/class/extcon/.../state shows the cable attach/detach
> +		information of the corresponding extcon object. If the extcon
> +		objecct has an optional callback "show_state" defined, the
> +		callback will provide the name with this sysfs node.
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index d236aef..0233ad9 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -140,4 +140,6 @@ source "drivers/virt/Kconfig"
>  
>  source "drivers/devfreq/Kconfig"
>  
> +source "drivers/extcon/Kconfig"
> +
>  endmenu
> diff --git a/drivers/Makefile b/drivers/Makefile
> index 95952c8..c41dfa9 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -134,3 +134,4 @@ obj-$(CONFIG_VIRT_DRIVERS)	+= virt/
>  obj-$(CONFIG_HYPERV)		+= hv/
>  
>  obj-$(CONFIG_PM_DEVFREQ)	+= devfreq/
> +obj-$(CONFIG_EXTCON)		+= extcon/
> diff --git a/drivers/extcon/Kconfig b/drivers/extcon/Kconfig
> new file mode 100644
> index 0000000..7932e1b
> --- /dev/null
> +++ b/drivers/extcon/Kconfig
> @@ -0,0 +1,17 @@
> +menuconfig EXTCON
> +	tristate "External Connector Class (extcon) support"
> +	help
> +	  Say Y here to enable external connector class (extcon) support.
> +	  This allows monitoring external connectors by userspace
> +	  via sysfs and uevent and supports external connectors with
> +	  multiple states; i.e., an extcon that may have multiple
> +	  cables attached. For example, an external connector of a device
> +	  may be used to connect an HDMI cable and a AC adaptor, and to
> +	  host USB ports. Many of 30-pin connectors including PDMI are
> +	  also good examples.
> +
> +if EXTCON
> +
> +comment "Extcon Device Drivers"
> +
> +endif # MULTISTATE_SWITCH
> diff --git a/drivers/extcon/Makefile b/drivers/extcon/Makefile
> new file mode 100644
> index 0000000..6bc6921
> --- /dev/null
> +++ b/drivers/extcon/Makefile
> @@ -0,0 +1,5 @@
> +#
> +# Makefile for external connector class (extcon) devices
> +#
> +
> +obj-$(CONFIG_EXTCON)		+= extcon_class.o
> diff --git a/drivers/extcon/extcon_class.c b/drivers/extcon/extcon_class.c
> new file mode 100644
> index 0000000..3c46368
> --- /dev/null
> +++ b/drivers/extcon/extcon_class.c
> @@ -0,0 +1,236 @@
> +/*
> + *  drivers/extcon/extcon_class.c
> + *
> + *  External connector (extcon) class driver
> + *
> + * Copyright (C) 2012 Samsung Electronics
> + * Author: Donggeun Kim <dg77.kim@...sung.com>
> + * Author: MyungJoo Ham <myungjoo.ham@...sung.com>
> + *
> + * based on android/drivers/switch/switch_class.c
> + * Copyright (C) 2008 Google, Inc.
> + * Author: Mike Lockwood <lockwood@...roid.com>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * 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.
> + *
> +*/
> +
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/init.h>
> +#include <linux/device.h>
> +#include <linux/fs.h>
> +#include <linux/err.h>
> +#include <linux/extcon.h>
> +#include <linux/slab.h>
> +
> +struct class *extcon_class;
> +#if defined(CONFIG_ANDROID) && !defined(CONFIG_ANDROID_SWITCH)
> +static struct class_compat *switch_class;
> +#endif /* CONFIG_ANDROID && !defined(CONFIG_ANDROID_SWITCH) */
> +
> +static ssize_t state_show(struct device *dev, struct device_attribute *attr,
> +			  char *buf)
> +{
> +	struct extcon_dev *edev = (struct extcon_dev *) dev_get_drvdata(dev);

Shouldn't need the cast. Same elsewhere.

> +
> +	if (edev->print_state) {
> +		int ret = edev->print_state(edev, buf);
> +
> +		if (ret >= 0)
> +			return ret;
> +		/* Use default if failed */
> +	}
> +	return sprintf(buf, "%u\n", edev->state);
> +}
> +
> +static ssize_t name_show(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	struct extcon_dev *edev = (struct extcon_dev *) dev_get_drvdata(dev);
> +
> +	/* Optional callback given by the user */
> +	if (edev->print_name) {
> +		int ret = edev->print_name(edev, buf);
> +		if (ret >= 0)
> +			return ret;
> +	}
> +
> +	return sprintf(buf, "%s\n", dev_name(edev->dev));
> +}
> +
> +/**
> + * extcon_set_state() - Set the cable attach states of the extcon device.
> + * @edev:	the extcon device
> + * @state:	new cable attach status for @edev
> + *
> + * Changing the state sends uevent with environment variable containing
> + * the name of extcon device (envp[0]) and the state output (envp[1]).
> + * Tizen uses this format for extcon device to get events from ports.
> + * Android uses this format as well.
> + */
> +void extcon_set_state(struct extcon_dev *edev, u32 state)
> +{
> +	char name_buf[120];
> +	char state_buf[120];

Where do these sizes come from?

> +	char *prop_buf;
> +	char *envp[3];
> +	int env_offset = 0;
> +	int length;
> +
> +	if (edev->state != state) {
> +		edev->state = state;
> +
> +		prop_buf = (char *)get_zeroed_page(GFP_KERNEL);
> +		if (prop_buf) {

	if (!prop_buf) {
		dev_err(edev->dev, "out of memory in extcon_set_state\n");
		kobject_uevent(&edev->dev->kobj, KOBJ_CHANGE);
		return;
	}


Gives you one less level of indentation for the normal execution path.
Also, is there a good reason to use get_zeroed_page(...) instead of
kzalloc(PAGE_SIZE, ...), the latter doesn't require casting.

Also, should this function return an int so that callers can know
whether it actually succeeded?

> +			length = name_show(edev->dev, NULL, prop_buf);
> +			if (length > 0) {
> +				if (prop_buf[length - 1] == '\n')
> +					prop_buf[length - 1] = 0;

This is a bit ugly using a sysfs show function internally and then
manually cropping out the '\n'. Why not have a name get function:

	static ssize_t extcon_snprint_name(struct extcon_dev *edev, char *buf, size_t buf_size)
	{
		int ret;

		if (edev->print_state) {
			ret = edev->print_state(edev, buf, buf_size);
			if (ret >= 0)
				return ret;
		}
		return snprintf(buf, buf_size, "%u", edev->state);
	}


This function and the sysfs show function can call extcon_snprint_name.
Having an explict size would also get rid of the need for the
intermediate prop_buf here:

	count = snprintf(name_buf, sizeof(name_buf), "NAME=");
	extcon_snprint_name(edev, name_buf + count, sizeof(name_buf) - count);


> +				snprintf(name_buf, sizeof(name_buf),
> +					"NAME=%s", prop_buf);
> +				envp[env_offset++] = name_buf;
> +			}
> +			length = state_show(edev->dev, NULL, prop_buf);
> +			if (length > 0) {
> +				if (prop_buf[length - 1] == '\n')
> +					prop_buf[length - 1] = 0;
> +				snprintf(state_buf, sizeof(state_buf),
> +					"STATE=%s", prop_buf);
> +				envp[env_offset++] = state_buf;
> +			}
> +			envp[env_offset] = NULL;
> +			kobject_uevent_env(&edev->dev->kobj, KOBJ_CHANGE, envp);
> +			free_page((unsigned long)prop_buf);
> +		} else {
> +			dev_err(edev->dev, "out of memory in extcon_set_state\n");
> +			kobject_uevent(&edev->dev->kobj, KOBJ_CHANGE);
> +		}
> +	}
> +}
> +EXPORT_SYMBOL_GPL(extcon_set_state);
> +
> +static struct device_attribute extcon_attrs[] = {
> +	__ATTR_RO(state),
> +	__ATTR_RO(name),
> +};
> +
> +static int create_extcon_class(void)
> +{
> +	if (!extcon_class) {

extcon_class can only ever be NULL since this function is only ever
called from the module init function right?

> +		extcon_class = class_create(THIS_MODULE, "extcon");
> +		if (IS_ERR(extcon_class))
> +			return PTR_ERR(extcon_class);
> +		extcon_class->dev_attrs = extcon_attrs;
> +
> +#if defined(CONFIG_ANDROID) && !defined(CONFIG_ANDROID_SWITCH)
> +		switch_class = class_compat_register("switch");
> +		if (WARN(!switch_class, "cannot allocate"))
> +			return -ENOMEM;
> +#endif /* CONFIG_ANDROID && !defined(CONFIG_ANDROID_SWITCH) */

This is a bit ugly putting Android specific hacks in mainline. Is this
something that Android could do in user-space instead?

> +	}
> +
> +	return 0;
> +}
> +
> +static void extcon_cleanup(struct extcon_dev *edev, bool skip)
> +{
> +	if (!skip && get_device(edev->dev)) {
> +		device_unregister(edev->dev);
> +		put_device(edev->dev);
> +	}
> +
> +	kfree(edev->dev);
> +}
> +
> +static void extcon_dev_release(struct device *dev)
> +{
> +	struct extcon_dev *edev = (struct extcon_dev *) dev_get_drvdata(dev);
> +

Don't need the cast.

> +	extcon_cleanup(edev, true);
> +}
> +
> +/**
> + * extcon_dev_register() - Register a new extcon device
> + * @edev	: the new extcon device (should be allocated before calling)
> + * @dev		: the parent device for this extcon device.
> + *
> + * Among the members of edev struct, please set the "user initializing data"
> + * in any case and set the "optional callbacks" if required. However, please
> + * do not set the values of "internal data", which are initialized by
> + * this function.
> + */
> +int extcon_dev_register(struct extcon_dev *edev, struct device *dev)
> +{
> +	int ret;
> +
> +	if (!extcon_class) {
> +		ret = create_extcon_class();
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	edev->dev = kzalloc(sizeof(struct device), GFP_KERNEL);

	if (!evdev->dev) {
		/* Explode */
	}


> +	edev->dev->parent = dev;
> +	edev->dev->class = extcon_class;
> +	edev->dev->release = extcon_dev_release;
> +
> +	dev_set_name(edev->dev, edev->name ? edev->name : dev_name(dev));
> +	ret = device_register(edev->dev);
> +	if (ret) {
> +		put_device(edev->dev);
> +		goto err_dev;
> +	}
> +#if defined(CONFIG_ANDROID) && !defined(CONFIG_ANDROID_SWITCH)
> +	if (switch_class)
> +		ret = class_compat_create_link(switch_class, edev->dev,
> +					       dev);
> +#endif /* CONFIG_ANDROID && !defined(CONFIG_ANDROID_SWITCH) */
> +
> +	dev_set_drvdata(edev->dev, edev);
> +	edev->state = 0;
> +	return 0;
> +
> +err_dev:
> +	kfree(edev->dev);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(extcon_dev_register);
> +
> +/**
> + * extcon_dev_unregister() - Unregister the extcon device.
> + * @edev:	the extcon device instance to be unregitered.
> + *
> + * Note that this does not call kfree(edev) because edev was not allocated
> + * by this class.
> + */
> +void extcon_dev_unregister(struct extcon_dev *edev)
> +{
> +	extcon_cleanup(edev, false);
> +}
> +EXPORT_SYMBOL_GPL(extcon_dev_unregister);
> +
> +static int __init extcon_class_init(void)
> +{
> +	return create_extcon_class();
> +}
> +module_init(extcon_class_init);
> +
> +static void __exit extcon_class_exit(void)
> +{
> +	class_destroy(extcon_class);
> +}
> +module_exit(extcon_class_exit);
> +
> +MODULE_AUTHOR("Mike Lockwood <lockwood@...roid.com>");
> +MODULE_AUTHOR("Donggeun Kim <dg77.kim@...sung.com>");
> +MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@...sung.com>");
> +MODULE_DESCRIPTION("External connector (extcon) class driver");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/extcon.h b/include/linux/extcon.h
> new file mode 100644
> index 0000000..9cb3aaa
> --- /dev/null
> +++ b/include/linux/extcon.h
> @@ -0,0 +1,82 @@
> +/*
> + *  External connector (extcon) class driver
> + *
> + * Copyright (C) 2012 Samsung Electronics
> + * Author: Donggeun Kim <dg77.kim@...sung.com>
> + * Author: MyungJoo Ham <myungjoo.ham@...sung.com>
> + *
> + * based on switch class driver
> + * Copyright (C) 2008 Google, Inc.
> + * Author: Mike Lockwood <lockwood@...roid.com>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * 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.
> + *
> +*/
> +
> +#ifndef __LINUX_EXTCON_H__
> +#define __LINUX_EXTCON_H__
> +
> +/**
> + * struct extcon_dev - An extcon device represents one external connector.
> + * @name	The name of this extcon device. Parent device name is used
> + *		if NULL.
> + * @print_name	An optional callback to override the method to print the
> + *		name of the extcon device.
> + * @print_state	An optional callback to override the method to print the
> + *		status of the extcon device.
> + * @dev		Device of this extcon. Do not provide at register-time.
> + * @state	Attach/detach state of this extcon. Do not provide at
> + *		register-time
> + *
> + * In most cases, users only need to provide "User initializing data" of
> + * this struct when registering an extcon. In some exceptional cases,
> + * optional callbacks may be needed. However, the values in "internal data"
> + * are overwritten by register function.
> + */
> +struct extcon_dev {
> +	/* --- Optional user initializing data --- */
> +	const char	*name;
> +
> +	/* --- Optional callbacks to override class functions --- */
> +	ssize_t	(*print_name)(struct extcon_dev *edev, char *buf);
> +	ssize_t	(*print_state)(struct extcon_dev *edev, char *buf);
> +
> +	/* --- Internal data. Please do not set. --- */
> +	struct device	*dev;
> +	u32		state;
> +};
> +
> +#if IS_ENABLED(CONFIG_EXTCON)
> +extern int extcon_dev_register(struct extcon_dev *edev, struct device *dev);
> +extern void extcon_dev_unregister(struct extcon_dev *edev);
> +
> +static inline u32 extcon_get_state(struct extcon_dev *edev)
> +{
> +	return edev->state;
> +}
> +
> +extern void extcon_set_state(struct extcon_dev *edev, u32 state);
> +#else /* CONFIG_EXTCON */
> +static inline int extcon_dev_register(struct extcon_dev *edev,
> +				      struct device *dev)
> +{
> +	return 0;
> +}
> +
> +static inline void extcon_dev_unregister(struct extcon_dev *edev) { }
> +
> +static inline u32 extcon_get_state(struct extcon_dev *edev)
> +{
> +	return 0;
> +}
> +
> +static inline void extcon_set_state(struct extcon_dev *edev, u32 state) { }
> +#endif /* CONFIG_EXTCON */
> +#endif /* __LINUX_EXTCON_H__ */

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