From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:57819 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751916AbaE1DaV (ORCPT ); Tue, 27 May 2014 23:30:21 -0400 Date: Tue, 27 May 2014 20:30:19 -0700 From: Greg KH To: Bjorn Helgaas Cc: Alex Williamson , linux-pci@vger.kernel.org, kvm@vger.kernel.org, konrad.wilk@oracle.com, kim.phillips@linaro.org, stuart.yoder@freescale.com, agraf@suse.de, libvir-list@redhat.com, iommu@lists.linux-foundation.org, christoffer.dall@linaro.org, tech@virtualopensystems.com, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] PCI: Introduce new device binding path using pci_dev.driver_override Message-ID: <20140528033019.GA11547@kroah.com> References: <20140520145136.28232.90707.stgit@bling.home> <20140528030742.GO11907@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140528030742.GO11907@google.com> Sender: linux-pci-owner@vger.kernel.org List-ID: On Tue, May 27, 2014 at 09:07:42PM -0600, Bjorn Helgaas wrote: > On Tue, May 20, 2014 at 08:53:21AM -0600, Alex Williamson wrote: > > The driver_override field allows us to specify the driver for a device > > rather than relying on the driver to provide a positive match of the > > device. This shortcuts the existing process of looking up the vendor > > and device ID, adding them to the driver new_id, binding the device, > > then removing the ID, but it also provides a couple advantages. > > > > First, the above existing process allows the driver to bind to any > > device matching the new_id for the window where it's enabled. This is > > often not desired, such as the case of trying to bind a single device > > to a meta driver like pci-stub or vfio-pci. Using driver_override we > > can do this deterministically using: > > > > echo pci-stub > /sys/bus/pci/devices/0000:03:00.0/driver_override > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > > > Previously we could not invoke drivers_probe after adding a device > > to new_id for a driver as we get non-deterministic behavior whether > > the driver we intend or the standard driver will claim the device. > > Now it becomes a deterministic process, only the driver matching > > driver_override will probe the device. > > > > To return the device to the standard driver, we simply clear the > > driver_override and reprobe the device: > > > > echo > /sys/bus/pci/devices/0000:03:00.0/driver_override > > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > > > Another advantage to this approach is that we can specify a driver > > override to force a specific binding or prevent any binding. For > > instance when an IOMMU group is exposed to userspace through VFIO > > we require that all devices within that group are owned by VFIO. > > However, devices can be hot-added into an IOMMU group, in which case > > we want to prevent the device from binding to any driver (override > > driver = "none") or perhaps have it automatically bind to vfio-pci. > > With driver_override it's a simple matter for this field to be set > > internally when the device is first discovered to prevent driver > > matches. > > > > Signed-off-by: Alex Williamson > > Cc: Greg Kroah-Hartman > > Greg, are you going to weigh in on this? It does seem to solve some real > problems. ISTR you had an opinion once, but I don't know your current > thoughts. Give me a few more days, still digging through my patch backlog... thanks, greg k-h