Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754753AbYLJNIm (ORCPT ); Wed, 10 Dec 2008 08:08:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752033AbYLJNIb (ORCPT ); Wed, 10 Dec 2008 08:08:31 -0500 Received: from mga03.intel.com ([143.182.124.21]:21821 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751657AbYLJNIa (ORCPT ); Wed, 10 Dec 2008 08:08:30 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.33,747,1220252400"; d="scan'208";a="88594410" Date: Wed, 10 Dec 2008 20:43:11 +0800 From: Wu Fengguang To: Laurent Pinchart Cc: LKML , Greg Kroah-Hartman , "linux-usb@vger.kernel.org" Subject: Re: [PATCH] USB: use stack allocation for struct usb_ctrlrequest Message-ID: <20081210124308.GB6772@localhost> References: <20081210073247.GA18630@localhost> <200812101040.09886.laurent.pinchart@skynet.be> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200812101040.09886.laurent.pinchart@skynet.be> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2396 Lines: 72 Hi Laurent, On Wed, Dec 10, 2008 at 11:40:09AM +0200, Laurent Pinchart wrote: > Hi Wu, > > On Wednesday 10 December 2008, Wu Fengguang wrote: > > sizeof(struct usb_ctrlrequest) = 8, which is as small as the *dt pointer > > in a 64bit system. > > The usb_ctrlrequest pointer is passed down to the hardware and must point to > DMA-able memory. For this reason you can't use the stack and must kmalloc() > the structure. Ah thanks for the background. Does GFP_NOIO guarantee that? e.g. what if the memory is allocated from ZONE_HIGHMEM? Thanks, Fengguang > > > Cc: Greg Kroah-Hartman > > Signed-off-by: Wu Fengguang > > --- > > drivers/usb/core/message.c | 27 ++++++++------------------- > > 1 file changed, 8 insertions(+), 19 deletions(-) > > > > --- linux-2.6.orig/drivers/usb/core/message.c > > +++ linux-2.6/drivers/usb/core/message.c > > @@ -130,26 +130,15 @@ int usb_control_msg(struct usb_device *d > > __u8 requesttype, __u16 value, __u16 index, void *data, > > __u16 size, int timeout) > > { > > - struct usb_ctrlrequest *dr; > > - int ret; > > - > > - dr = kmalloc(sizeof(struct usb_ctrlrequest), GFP_NOIO); > > - if (!dr) > > - return -ENOMEM; > > - > > - dr->bRequestType = requesttype; > > - dr->bRequest = request; > > - dr->wValue = cpu_to_le16p(&value); > > - dr->wIndex = cpu_to_le16p(&index); > > - dr->wLength = cpu_to_le16p(&size); > > + struct usb_ctrlrequest dr = { > > + .bRequestType = requesttype, > > + .bRequest = request, > > + .wValue = cpu_to_le16p(&value), > > + .wIndex = cpu_to_le16p(&index), > > + .wLength = cpu_to_le16p(&size), > > + }; > > > > - /* dbg("usb_control_msg"); */ > > - > > - ret = usb_internal_control_msg(dev, pipe, dr, data, size, timeout); > > - > > - kfree(dr); > > - > > - return ret; > > + return usb_internal_control_msg(dev, pipe, &dr, data, size, timeout); > > } > > EXPORT_SYMBOL_GPL(usb_control_msg); > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-usb" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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/