Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946105AbbHGRxU (ORCPT ); Fri, 7 Aug 2015 13:53:20 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37370 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946081AbbHGRxS (ORCPT ); Fri, 7 Aug 2015 13:53:18 -0400 Date: Fri, 7 Aug 2015 10:53:17 -0700 From: Greg KH To: Baolin Wang Cc: Peter Chen , Felipe Balbi , Mark Brown , LKML , "sojka@merica.cz" , Alan Stern , "andreas@gaisler.com" , "linux-usb@vger.kernel.org" Subject: Re: [PATCH 2/2] gadget: Support for the usb charger framework Message-ID: <20150807175317.GD10003@kroah.com> References: <8fcb9ff7a8e01bec53813f0702ff606bf4982943.1438844454.git.baolin.wang@linaro.org> <20150807054554.GE13200@shlinux2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23+102 (2ca89bed6448) (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1818 Lines: 48 On Fri, Aug 07, 2015 at 05:22:47PM +0800, Baolin Wang wrote: > On 7 August 2015 at 17:07, Peter Chen 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. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/