From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753657AbbEEWN5 (ORCPT ); Tue, 5 May 2015 18:13:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34082 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752091AbbEEWNx (ORCPT ); Tue, 5 May 2015 18:13:53 -0400 Date: Mon, 4 May 2015 10:14:51 +0200 From: Greg Kroah-Hartman To: Lu Baolu Cc: Mathias Nyman , Alan Stern , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH 1/3] usb: add a hcd notify entry in hc_driver Message-ID: <20150504081451.GA8436@kroah.com> References: <1430709332-18814-1-git-send-email-baolu.lu@linux.intel.com> <1430709332-18814-2-git-send-email-baolu.lu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1430709332-18814-2-git-send-email-baolu.lu@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 04, 2015 at 11:15:30AM +0800, Lu Baolu wrote: > This patch adds a new entry pointer in hc_driver. With this new entry, > USB core can notify host driver when something happens and host driver > is willing to be notified. One use case of this interface comes from > xHCI compatible host controller driver. > > The xHCI spec is designed to allow an xHC implementation to cache the > endpoint state. Caching endpoint state allows an xHC to reduce latency > when handling ERDYs and other USB asynchronous events. However holding > this state in xHC consumes resources and power. The xHCI spec designs > some methods through which host controller driver can hint xHC about > how to optimize its operation, e.g. to determine when it holds state > internally or pushes it out to memory, when to power down logic, etc. > > When a USB device is going to suspend, states of all endpoints cached > in the xHC should be pushed out to memory to save power and resources. > Vice versa, when a USB device resumes, those states should be brought > back to the cache. USB core suspends or resumes a USB device by sending > set/clear port feature requests to the parent hub where the USB device > is connected. Unfortunately, these operations are transparent to xHCI > driver unless the USB device is plugged in a root port. This patch > utilizes the notify interface to notify xHCI driver whenever a USB > device's power state is changed. > > It is harmless if a USB devices under USB 3.0 host controller suspends > or resumes without a notification to hcd driver. However there may be > less opportunities for power savings and there may be increased latency > for restarting an endpoint. The precise impact will be different for > each xHC implementation. It all depends on what an implementation does > with the hints. > > Signed-off-by: Lu Baolu > --- > drivers/usb/core/generic.c | 10 ++++++++-- > drivers/usb/core/hcd.c | 23 +++++++++++++++++++++++ > include/linux/usb/hcd.h | 11 ++++++++++- > 3 files changed, 41 insertions(+), 3 deletions(-) > > diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c > index 358ca8d..92bee33 100644 > --- a/drivers/usb/core/generic.c > +++ b/drivers/usb/core/generic.c > @@ -211,8 +211,12 @@ static int generic_suspend(struct usb_device *udev, pm_message_t msg) > /* Non-root devices don't need to do anything for FREEZE or PRETHAW */ > else if (msg.event == PM_EVENT_FREEZE || msg.event == PM_EVENT_PRETHAW) > rc = 0; > - else > + else { > + hcd_notify(udev, HCD_MSG_DEV_SUSPEND, &msg); > rc = usb_port_suspend(udev, msg); > + if (rc) > + hcd_notify(udev, HCD_MSG_DEV_RESUME, &msg); > + } > > return rc; > } > @@ -228,8 +232,10 @@ static int generic_resume(struct usb_device *udev, pm_message_t msg) > */ > if (!udev->parent) > rc = hcd_bus_resume(udev, msg); > - else > + else { > rc = usb_port_resume(udev, msg); > + hcd_notify(udev, HCD_MSG_DEV_RESUME, &msg); > + } > return rc; > } > > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c > index 45a915c..725d611 100644 > --- a/drivers/usb/core/hcd.c > +++ b/drivers/usb/core/hcd.c > @@ -2289,6 +2289,29 @@ void usb_hcd_resume_root_hub (struct usb_hcd *hcd) > } > EXPORT_SYMBOL_GPL(usb_hcd_resume_root_hub); > > +/** > + * hcd_notify - notify hcd driver with a message > + * @udev: USB device > + * @type: message type of this notification > + * @data: message type specific data > + * > + * Call back to hcd driver to notify an event. > + */ > +void hcd_notify(struct usb_device *udev, > + enum hcd_notification_type type, void *data) > +{ > + struct usb_hcd *hcd; > + > + if (!udev) > + return; > + > + hcd = bus_to_hcd(udev->bus); > + > + if (hcd->driver->notify) > + hcd->driver->notify(hcd, udev, type, data); > +} > +EXPORT_SYMBOL_GPL(hcd_notify); Why does this have to be exported?