linux-kernel - Re: [PATCH 2/2] gadget: Support for the usb charger framework

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Date:	Fri, 7 Aug 2015 17:22:47 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Peter Chen <Peter.Chen@...escale.com>
Cc:	Felipe Balbi <balbi@...com>, Mark Brown <broonie@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"sojka@...ica.cz" <sojka@...ica.cz>,
	Alan Stern <stern@...land.harvard.edu>,
	"andreas@...sler.com" <andreas@...sler.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 2/2] gadget: Support for the usb charger framework

On 7 August 2015 at 17:07, Peter Chen <Peter.Chen@...escale.com> wrote:
>
>> >>  /**
>> >>   * struct usb_udc - describes one usb device controller @@ -127,12
>> >> +128,45 @@ void usb_gadget_giveback_request(struct usb_ep *ep,  }
>> >> EXPORT_SYMBOL_GPL(usb_gadget_giveback_request);
>> >>
>> >> +int usb_gadget_register_notify(struct usb_gadget *gadget,
>> >> +                            struct notifier_block *nb) {
>> >> +     unsigned long flags;
>> >> +     int ret;
>> >> +
>> >> +     spin_lock_irqsave(&gadget->lock, flags);
>> >
>> > I find you use so many spin_lock_irqsave, any reasons for that?
>> > Why mutex_lock can't be used?
>> >
>>
>> The spin_lock_irqsave() can make it as a atomic notifier, that can make sure the
>> gadget state event can be quickly reported to the user who register a notifier
>> on the gadget device. Is it OK?
>>
>
> I don't think it is a good reason, spin_lock_irqsave is usually used for protecting
> data which is accessed at atomic environment.
>

Yes, we want the notify process is a atomic environment which do not
want to be interrupted by irq or other things to make the notice can
be quickly reported to the user.

Also i think the notify process is less cost, thus i use the spinlock. Thanks.

> Peter



-- 
Baolin.wang
Best Regards
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