On Thu, Jul 16, 2009 at 03:31:01PM +0300, Michael S. Tsirkin wrote: > On Wed, Jul 15, 2009 at 03:08:29PM -0700, Greg KH wrote: > > On Wed, Jul 15, 2009 at 11:13:40PM +0300, Michael S. Tsirkin wrote: > > > This adds a generic uio driver that can bind to any PCI device. First > > > user will be virtualization where a qemu userspace process needs to give > > > guest OS access to the device. > > > > > > Interrupts are handled using the Interrupt Disable bit in the PCI command > > > register and Interrupt Status bit in the PCI status register. All devices > > > compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should > > > support these bits. Driver detects this support, and won't bind to devices > > > which do not support the Interrupt Disable Bit in the command register. > > > > > > It's expected that more features of interest to virtualization will be > > > added to this driver in the future. Possibilities are: mmap for device > > > resources, MSI/MSI-X, eventfd (to interface with kvm), iommu. > > > > > > Acked-by: Chris Wright <chrisw@xxxxxxxxxx> > > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > --- > > > > > > Hans, Greg, please review and consider for upstream. > > > > > > This is intended to solve the problem in virtualization that shared > > > interrupts do not work with assigned devices. Earlier versions of this > > > patch have circulated on kvm@vger. > > > > How does this play with the pci-stub driver that I thought was written > > to solve this very problem? > > > AFAIK the problem pci stub was written to solve is simply to bind to a > device. You then have to use another kernel module which looks the > device up with something like pci_get_bus_and_slot to do anything > useful. In particular, for non-shared interrupts, we can disable the > interrupt in the apic. But this does not work well for shared > interrupts. Thus this work. > > The uio driver will be used in virtualization scenarious, a couple > of possible ones that have been mentioned on the kvm list are: > - device assignment (guest access to device) for simple devices with > shared interrupts: emulating PCI is tricky enough to better be done in > userspace. shared interrupt support is important as it happens > with real devices > - simple communication between guest and host: > we create a virtual device in host, and userspace > driver in guest gets events and passes them on > to e.g. dbus. shared interrupt support is important > to avoid wasting irqs Ah, ok, thanks for all of the explanation, that makes sense. greg k-h -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
