> From: Dong Jia > Sent: Monday, June 06, 2016 2:59 PM > [...] > Channel I/O is quite different to PCI, so I copied some more details > here. Hope these could help. > > Channel subsystem: > The channel subsystem directs the flow of information between I/O devices > and main storage. It relieves CPUs of the task of communicating directly > with I/O devices and permits data processing to proceed concurrently with > I/O processing. > > Channel path: > The channel subsystem uses one or more channel paths as the communication > link in managing the flow of information to or from I/O devices. > > Subchannel: > Within the channel subsystem are subchannels. One subchannel of type I/O > is provided for and dedicated to each I/O device accessible to the channel > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > subsystem. > > Control unit: > A control unit implements a standardized interface which translates between > the Channel Subsystem and the actual device. It does this by adapting the > characteristics of each device so that it can respond to the standard form > of control provided by the channel subsystem. > > Channel Path: > The channel subsystem communicates with the I/O devices by means of > channel paths between the channel subsystem and control units. > > +-------------------+ > | channel subsystem | > +-------------------+ > | | > | +----------+ | +--------------+ +------------+ > | |subchannel| | channel path | control unit | | I/O device | > | +---------------------------------------------------------------+ > | | subchno | | | | | devno | > | +----------+ | +--------------+ +------------+ > | | > +-------------------+ > > There is no concept of ccw-device registers by the subchannel. Control > unit will interact with the device, collect the I/O result, and inform > the result to the subchannel. > So it seems to me, there is no needs to provide region info for > isolation. As mentioned above, the isolation is quite natural. > > Please correct me in case I misunderstood some of the concepts in your > questions and gave irrelevant answers. :> > Thanks for above background which is very useful. Several follow-up Qs: 1) Does it mean that VFIO is managing resource in subchannel level, so Qemu can only operate subchannels assigned to itself (then emulate as the complete channel io sub-system to guest)? 2) How are ccw commands associated with a subchannel? Are they submitted through a dedicated subchannel interface (so VFIO can easily map that interface) or that subchannel is specified by a special ccw cmd (means VFIO-ccw needs to scan cmds to avoid malicious attempts on non-assigned subchannels)? Thanks Kevin -- 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
