Re: [PATCH 1/2] gadget: Introduce the usb charger framework

[Greg KH]

On Thu, Aug 06, 2015 at 03:03:48PM +0800, Baolin Wang wrote:
> This patch introduces the usb charger driver based on usb gadget that
> makes an enhancement to a power driver. It works well in practice but
> that requires a system with suitable hardware.
> 
> The basic conception of the usb charger is that, when one usb charger
> is added or removed by reporting from the usb gadget state change or
> the extcon device state change, the usb charger will report to power
> user to set the current limitation.
> 
> The usb charger will register notifiees on the usb gadget or the extcon
> device to get notified the usb charger state.
> 
> Power user will register a notifiee on the usb charger to get notified
> by status changes from the usb charger. It will report to power user
> to set the current limitation when detecting the usb charger is added
> or removed from extcon device state or usb gadget state.
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
> ---
>  drivers/usb/gadget/charger.c    |  547 +++++++++++++++++++++++++++++++++++++++
>  include/linux/usb/usb_charger.h |  101 ++++++++
>  2 files changed, 648 insertions(+)
>  create mode 100644 drivers/usb/gadget/charger.c
>  create mode 100644 include/linux/usb/usb_charger.h
> 
> diff --git a/drivers/usb/gadget/charger.c b/drivers/usb/gadget/charger.c
> new file mode 100644
> index 0000000..3ca0180
> --- /dev/null
> +++ b/drivers/usb/gadget/charger.c
> @@ -0,0 +1,547 @@
> +/*
> + * usb charger.c -- USB charger driver
> + *
> + * 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.

I have to ask, do you really mean "any later version"?

> + */
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/extcon.h>
> +#include <linux/export.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/usb.h>
> +#include <linux/usb/ch9.h>
> +#include <linux/usb/gadget.h>
> +#include <linux/usb/usb_charger.h>
> +
> +#define DEFAULT_CUR_PROTECT	(50)
> +#define DEFAULT_SDP_CUR_LIMIT	(500 - DEFAULT_CUR_PROTECT)
> +#define DEFAULT_DCP_CUR_LIMIT	(1500 - DEFAULT_CUR_PROTECT)
> +#define DEFAULT_CDP_CUR_LIMIT	(1500 - DEFAULT_CUR_PROTECT)
> +#define DEFAULT_ACA_CUR_LIMIT	(1500 - DEFAULT_CUR_PROTECT)
> +
> +static LIST_HEAD(usb_charger_list);
> +static DEFINE_MUTEX(usb_charger_list_lock);
> +
> +/*
> + * usb_charger_find_by_name - Get the usb charger device by name.
> + * @name - usb charger device name.
> + *
> + * notes: when this function walks the list and returns a charger
> + * it's dropped the lock which means that something else could come
> + * along and delete the charger before we dereference the pointer.
> + * It's very unlikely but it's a possibility so you should take care
> + * of it.
> + * Thus when you get the usb charger by name, you should call
> + * put_usb_charger() to derease the reference count of the usb charger.
> + *
> + * return the instance of usb charger device.
> + */
> +struct usb_charger *usb_charger_find_by_name(char *name)
> +{
> +	struct usb_charger *uchger;
> +
> +	if (!name)
> +		return ERR_PTR(-EINVAL);
> +
> +	mutex_lock(&usb_charger_list_lock);
> +	list_for_each_entry(uchger, &usb_charger_list, entry) {
> +		if (!strcmp(uchger->name, name)) {
> +			get_usb_charger(uchger);
> +			mutex_unlock(&usb_charger_list_lock);
> +			return uchger;
> +		}
> +	}
> +	mutex_unlock(&usb_charger_list_lock);
> +
> +	return NULL;
> +}
> +
> +/*
> + * usb_charger_register_notify() - Register a notifiee to get notified by
> + * 		any attach status changes from the usb charger type detection.
> + * @uchger - the usb charger device which is monitored.
> + * @nb - a notifier block to be registered.
> + */
> +void usb_charger_register_notify(struct usb_charger *uchger,
> +				 struct notifier_block *nb)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&uchger->lock, flags);
> +	raw_notifier_chain_register(&uchger->uchger_nh, nb);
> +	spin_unlock_irqrestore(&uchger->lock, flags);
> +}
> +
> +/*
> + * usb_charger_unregister_notify() - Unregister a notifiee from the usb charger.
> + * @uchger - the usb charger device which is monitored.
> + * @nb - a notifier block to be unregistered.
> + */
> +void usb_charger_unregister_notify(struct usb_charger *uchger,
> +				   struct notifier_block *nb)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&uchger->lock, flags);
> +	raw_notifier_chain_unregister(&uchger->uchger_nh, nb);
> +	spin_unlock_irqrestore(&uchger->lock, flags);
> +}
> +
> +/*
> + * usb_charger_register_extcon_notifier() - Register a notifiee of the usb
> + * 		charger to get notified by any attach status changes from
> + * 		the extcon device.
> + * @uchger - the usb charger device.
> + * @edev - the extcon device.
> + * @extcon_id - extcon id.
> + */
> +int usb_charger_register_extcon_notifier(struct usb_charger *uchger,
> +					 struct extcon_dev *edev,
> +					 unsigned int extcon_id)
> +{
> +	if (!uchger || !edev)
> +		return -EINVAL;
> +
> +	return extcon_register_notifier(edev, extcon_id, &uchger->extcon_nb.nb);
> +}

Why do we need wrappers around extcon?  I thought extcon was supposed to
do all of this for us, why are we putting another layer on top of it?

> +static void usb_charger_release(struct device *dev)
> +{
> +	struct usb_charger *uchger = dev_get_drvdata(dev);
> +
> +	if (!atomic_dec_and_test(&uchger->count)) {
> +		dev_err(dev, "The usb charger is still in use\n");

Why is the "count" different from the reference count?  You shouldn't be
in this function if the reference count is not 0, so tie your "user"
count to this one.  Having two different reference counts is a nightmare
and almost impossible to get right.  And a huge red flag that the design
is incorrect.

> +		return;

You can't "fail" a release call, so you just leaked memory all over the
floor here :(

> +/*
> + * usb_charger_register() - Register a new usb charger device.
> + * @uchger - the new usb charger device.

No, you should create the new charger device, as this subsystem now owns
the life cycle.  Don't rely on someone else to pass you an already
created structure.

> + *
> + */
> +int usb_charger_register(struct device *dev, struct usb_charger *uchger)
> +{
> +	static atomic_t uchger_no = ATOMIC_INIT(-1);

Use an idr/ida structure, don't try to roll your own logic here for
stuff that was long done for you.


> +	struct usb_charger *tmp;
> +	int ret;
> +
> +	if (!uchger) {
> +		dev_err(dev, "no device provided for charger\n");
> +		return -EINVAL;
> +	}
> +
> +	uchger->dev.parent = dev;
> +	uchger->dev.release = usb_charger_release;
> +	dev_set_name(&uchger->dev, "usb-chger%lu",
> +		     (unsigned long)atomic_inc_return(&uchger_no));
> +
> +	ret = device_register(&uchger->dev);
> +	if (ret) {
> +		put_device(&uchger->dev);
> +		return ret;
> +	}
> +
> +	dev_set_drvdata(&uchger->dev, uchger);
> +
> +	mutex_lock(&usb_charger_list_lock);
> +	list_for_each_entry(tmp, &usb_charger_list, entry) {
> +		if (!(strcmp(tmp->name, uchger->name))) {
> +			mutex_unlock(&usb_charger_list_lock);
> +			ret = -EEXIST;
> +			goto out;
> +		}
> +	}
> +	list_add_tail(&uchger->entry, &usb_charger_list);

Why do you need a separate list?  This subsystem's bus structure should
own that list of devices, no need for a separate one (again, a huge red
flag that the design is not correct.)

I stopped here.  Please rebase on linux-next and resend.

thanks,

greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/