From: "Henrik Rydberg" <rydberg@euromail.se>
Date: Mon, 29 Oct 2012 19:22:53 +0100
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] Input: introduce managed input devices (add devres
 support)
Message-ID: <20121029182253.GA8015@polaris.bitmath.org>
References: <20121023053513.GA15642@core.coreip.homeip.net>
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Hi Dmitry Torokhov wrote:

> There is a demand from driver's writers to use managed devices framework
> for their drivers. Unfortunately up to this moment input devices did not
> provide support for managed devices and that lead to mixing two styles
> of resource management which usually introduced more bugs, such as
> manually unregistering input device but relying in devres to free
> interrupt handler which (unless device is properly shut off) can cause
> ISR to reference already freed memory.
> 
> This change introduces devm_input_allocate_device() that will allocate
> managed instance of input device so that driver writers who prefer
> using devm_* framework do not have to mix 2 styles.
> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---

It seems devm always operates on the parent device, so strictly
speaking, the input device is not handled by devm, is that correct?
For instance, one cannot call devm_release_all() on the input device,
expecting the device to unregister itself from the input bus.

>  drivers/input/input.c | 175 ++++++++++++++++++++++++++++++++++++++++++--------
>  include/linux/input.h |   7 +-
>  2 files changed, 154 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/input/input.c b/drivers/input/input.c
> index 53a0dde..7fe74f8 100644
> --- a/drivers/input/input.c
> +++ b/drivers/input/input.c
> @@ -1723,7 +1723,7 @@ EXPORT_SYMBOL_GPL(input_class);
>  /**
>   * input_allocate_device - allocate memory for new input device
>   *
> - * Returns prepared struct input_dev or NULL.
> + * Returns prepared struct input_dev or %NULL.
>   *
>   * NOTE: Use input_free_device() to free devices that have not been
>   * registered; input_unregister_device() should be used for already
> @@ -1750,6 +1750,70 @@ struct input_dev *input_allocate_device(void)
>  }
>  EXPORT_SYMBOL(input_allocate_device);
>  
> +struct input_devres {
> +	struct input_dev *input;
> +};
> +
> +static int devm_input_device_match(struct device *dev, void *res, void *data)
> +{
> +	struct input_devres *devres = res;
> +
> +	return devres->input == data;
> +}
> +
> +static void devm_input_device_release(struct device *dev, void *res)
> +{
> +	struct input_devres *devres = res;
> +	struct input_dev *input = devres->input;
> +
> +	dev_dbg(dev, "%s: dropping reference to %s\n",
> +		__func__, dev_name(&input->dev));
> +	input_put_device(input);
> +}
> +
> +/**
> + * devm_input_allocate_device - allocate managed input device
> + * @dev: device owning the input device being created
> + *
> + * Returns prepared struct input_dev or %NULL.
> + *
> + * Managed input devices do not need to be explicitly unregistered or
> + * freed as it will be done automatically when owner device unbinds from
> + * its driver (or binding fails). Once managed input device is allocated,
> + * it is ready to be set up and registered in the same fashion as regular
> + * input device. There are no special devm_input_device_[un]register()
> + * variants, regular ones work with both managed and unmanaged devices.
> + *
> + * NOTE: the owner device is set up as parent of input device and users
> + * should not override it.
> + */
> +
> +struct input_dev *devm_input_allocate_device(struct device *dev)
> +{
> +	struct input_dev *input;
> +	struct input_devres *devres;
> +
> +	devres = devres_alloc(devm_input_device_release,
> +			      sizeof(struct input_devres), GFP_KERNEL);
> +	if (!devres)
> +		return NULL;
> +
> +	input = input_allocate_device();
> +	if (!input) {
> +		devres_free(devres);
> +		return NULL;
> +	}
> +
> +	input->dev.parent = dev;
> +	input->devres_managed = true;
> +
> +	devres->input = input;
> +	devres_add(dev, devres);
> +
> +	return input;
> +}
> +EXPORT_SYMBOL(devm_input_allocate_device);
> +
>  /**
>   * input_free_device - free memory occupied by input_dev structure
>   * @dev: input device to free
> @@ -1766,8 +1830,14 @@ EXPORT_SYMBOL(input_allocate_device);
>   */
>  void input_free_device(struct input_dev *dev)
>  {
> -	if (dev)
> +	if (dev) {
> +		if (dev->devres_managed)
> +			WARN_ON(devres_destroy(dev->dev.parent,
> +						devm_input_device_release,
> +						devm_input_device_match,
> +						dev));
>  		input_put_device(dev);

Device is put twice?

> +	}
>  }
>  EXPORT_SYMBOL(input_free_device);
>  
> @@ -1888,6 +1958,38 @@ static void input_cleanse_bitmasks(struct input_dev *dev)
>  	INPUT_CLEANSE_BITMASK(dev, SW, sw);
>  }
>  
> +static void __input_unregister_device(struct input_dev *dev)
> +{
> +	struct input_handle *handle, *next;
> +
> +	input_disconnect_device(dev);
> +
> +	mutex_lock(&input_mutex);
> +
> +	list_for_each_entry_safe(handle, next, &dev->h_list, d_node)
> +		handle->handler->disconnect(handle);
> +	WARN_ON(!list_empty(&dev->h_list));
> +
> +	del_timer_sync(&dev->timer);
> +	list_del_init(&dev->node);
> +
> +	input_wakeup_procfs_readers();
> +
> +	mutex_unlock(&input_mutex);
> +
> +	device_del(&dev->dev);
> +}
> +
> +static void devm_input_device_unregister(struct device *dev, void *res)
> +{
> +	struct input_devres *devres = res;
> +	struct input_dev *input = devres->input;
> +
> +	dev_dbg(dev, "%s: unregistering device %s\n",
> +		__func__, dev_name(&input->dev));
> +	__input_unregister_device(input);
> +}
> +
>  /**
>   * input_register_device - register device with input core
>   * @dev: device to be registered
> @@ -1903,11 +2005,21 @@ static void input_cleanse_bitmasks(struct input_dev *dev)
>  int input_register_device(struct input_dev *dev)
>  {
>  	static atomic_t input_no = ATOMIC_INIT(0);
> +	struct input_devres *devres = NULL;
>  	struct input_handler *handler;
>  	unsigned int packet_size;
>  	const char *path;
>  	int error;
>  
> +	if (dev->devres_managed) {
> +		devres = devres_alloc(devm_input_device_unregister,
> +				      sizeof(struct input_devres), GFP_KERNEL);
> +		if (!devres)
> +			return -ENOMEM;
> +
> +		devres->input = dev;
> +	}
> +
>  	/* Every input device generates EV_SYN/SYN_REPORT events. */
>  	__set_bit(EV_SYN, dev->evbit);
>  
> @@ -1923,8 +2035,10 @@ int input_register_device(struct input_dev *dev)
>  
>  	dev->max_vals = max(dev->hint_events_per_packet, packet_size) + 2;
>  	dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
> -	if (!dev->vals)
> -		return -ENOMEM;
> +	if (!dev->vals) {
> +		error = -ENOMEM;
> +		goto err_devres_free;
> +	}
>  
>  	/*
>  	 * If delay and period are pre-set by the driver, then autorepeating
> @@ -1949,7 +2063,7 @@ int input_register_device(struct input_dev *dev)
>  
>  	error = device_add(&dev->dev);
>  	if (error)
> -		return error;
> +		goto err_free_vals;
>  
>  	path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
>  	pr_info("%s as %s\n",
> @@ -1958,10 +2072,8 @@ int input_register_device(struct input_dev *dev)
>  	kfree(path);
>  
>  	error = mutex_lock_interruptible(&input_mutex);
> -	if (error) {
> -		device_del(&dev->dev);
> -		return error;
> -	}
> +	if (error)
> +		goto err_device_del;
>  
>  	list_add_tail(&dev->node, &input_dev_list);
>  
> @@ -1972,7 +2084,20 @@ int input_register_device(struct input_dev *dev)
>  
>  	mutex_unlock(&input_mutex);
>  
> +	if (dev->devres_managed) {
> +		dev_info(dev->dev.parent, "%s: registerign %s with devres.\n",
> +			__func__, dev->name ?: "N/A");
> +		devres_add(dev->dev.parent, devres);
> +	}

Why not add the resource to the input device instead? For one, it
would make the order of unregister and release more apparent. Right
now, the code seems to rely on the reverse for-loop in the devres
implementation.

>  	return 0;
> +
> +err_device_del:
> +	device_del(&dev->dev);
> +err_free_vals:
> +	kfree(dev->vals);
> +err_devres_free:
> +	devres_free(devres);
> +	return error;
>  }
>  EXPORT_SYMBOL(input_register_device);
>  
> @@ -1985,24 +2110,20 @@ EXPORT_SYMBOL(input_register_device);
>   */
>  void input_unregister_device(struct input_dev *dev)
>  {
> -	struct input_handle *handle, *next;
> -
> -	input_disconnect_device(dev);
> -
> -	mutex_lock(&input_mutex);
> -
> -	list_for_each_entry_safe(handle, next, &dev->h_list, d_node)
> -		handle->handler->disconnect(handle);
> -	WARN_ON(!list_empty(&dev->h_list));
> -
> -	del_timer_sync(&dev->timer);
> -	list_del_init(&dev->node);
> -
> -	input_wakeup_procfs_readers();
> -
> -	mutex_unlock(&input_mutex);
> -
> -	device_unregister(&dev->dev);
> +	if (dev->devres_managed) {
> +		WARN_ON(devres_destroy(dev->dev.parent,
> +					devm_input_device_unregister,
> +					devm_input_device_match,
> +					dev));
> +		__input_unregister_device(dev);

Unregistering twice?

> +		/*
> +		 * We do not do input_put_device() here because it will be done
> +		 * when 2nd devres fires up.
> +		 */
> +	} else {
> +		__input_unregister_device(dev);
> +		input_put_device(dev);
> +	}
>  }
>  EXPORT_SYMBOL(input_unregister_device);
>  
> diff --git a/include/linux/input.h b/include/linux/input.h
> index 15464ba..bfc479c 100644
> --- a/include/linux/input.h
> +++ b/include/linux/input.h
> @@ -1256,6 +1256,8 @@ struct input_value {
>   * @h_list: list of input handles associated with the device. When
>   *	accessing the list dev->mutex must be held
>   * @node: used to place the device onto input_dev_list
> + * @devres_managed: indicates that devices is managed with devres framework
> + *	and needs not be explicitly unregistered or freed.
>   */
>  struct input_dev {
>  	const char *name;
> @@ -1324,6 +1326,8 @@ struct input_dev {
>  	unsigned int num_vals;
>  	unsigned int max_vals;
>  	struct input_value *vals;
> +
> +	bool devres_managed;
>  };
>  #define to_input_dev(d) container_of(d, struct input_dev, dev)
>  
> @@ -1467,7 +1471,8 @@ struct input_handle {
>  	struct list_head	h_node;
>  };
>  
> -struct input_dev *input_allocate_device(void);
> +struct input_dev __must_check *input_allocate_device(void);
> +struct input_dev __must_check *devm_input_allocate_device(struct device *);
>  void input_free_device(struct input_dev *dev);
>  
>  static inline struct input_dev *input_get_device(struct input_dev *dev)
> -- 
> 1.7.11.7

Thanks,
Henrik
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