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

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Date:	Sat, 8 Aug 2015 14:23:31 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Peter Chen <Peter.Chen@...escale.com>, Felipe Balbi <balbi@...com>,
	Mark Brown <broonie@...nel.org>,
	LKML <linux-kernel@...r.kernel.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 8 August 2015 at 01:53, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Aug 07, 2015 at 05:22:47PM +0800, Baolin Wang wrote:
>> 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.
>
> No, this is a "slow" event, you don't need to notify anyone under atomic
> context, that's crazy.
>
>> Also i think the notify process is less cost, thus i use the spinlock. Thanks.
>
> No, use a mutex please, that's the safe thing.  This is not
> time-critical code at all.
>

OK, Thanks for your comments and will fix the lock thing.

> thanks,
>
> greg k-h



-- 
Baolin.wang
Best Regards
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