arch/s390/vfio-ccw.rst

8 Here we describe the vfio support for I/O subchannel devices for
13 I/O access method, which is so called Channel I/O. It has its own access
23 vfio framework. And we add read/write callbacks for special vfio I/O
25 (the real I/O subchannel device) to do further address translation and
26 to perform I/O instructions.
28 This document does not intend to explain the s390 I/O architecture in
31 - A good start to know Channel I/O in general:
32   https://en.wikipedia.org/wiki/Channel_I/O
47 paravirtualized virtio devices via the "Virtio Over Channel I/O
52 use the standard Channel I/O based mechanism, we also need to provide
71 defined access method and they are presenting I/O completion a unified
72 way: I/O interruptions.
74 All I/O requires the use of channel command words (CCWs). A CCW is an
75 instruction to a specialized I/O channel processor. A channel program is
76 a sequence of CCWs which are executed by the I/O channel subsystem.  To
80 operating system signals the I/O channel subsystem to begin executing
82 central processor is then free to proceed with non-I/O instructions
83 until interrupted. The I/O completion result is received by the
92   and starts the I/O with issuing a privileged Channel I/O instruction
95 - I/O completion will be signaled to the host with I/O interruptions.
104 Channel I/O does not have IOMMU hardware support, so the physical
107 Subchannel I/O instructions are all privileged instructions. When
108 handling the I/O instruction interception, vfio-ccw has the software
116   This is an I/O subchannel driver for the real subchannel device.  It
122   vfio_ccw also provides an I/O region to accept channel program
123   request from user space and store I/O interrupt result for user
124   space to retrieve. To notify user space an I/O completion, it offers
168 1. vfio_ccw.ko drives the physical I/O subchannel, and registers the
190 vfio-ccw I/O region
193 An I/O region is used to accept channel program request from user
194 space and store I/O interrupt result for user space to retrieve. The
209 While starting an I/O request, orb_area should be filled with the
213 irb_area stores the I/O result.
236   The channel path(s) used for the I/O were found to be not operational.
338   vfio_ccw, which is the driver for the I/O subchannel devices you want
348   This provides an I/O region, so that the user space program can pass a
352   notify the user space program the I/O completion in an asynchronous
357 bit more detail how an I/O request triggered by the QEMU guest will be
366     Get I/O region info during initialization.
369     Setup event notifier and handler to handle I/O completion.
376     Write the guest channel program and ORB to the I/O region.
394 	Interrupt handler gets the I/O result and write the result to
395 	the I/O region.
400     Get the signal and event handler reads out the result from the I/O
432 vfio-ccw supports classic (command mode) channel I/O only. Transport
441 2. ESA/390 Common I/O Device Commands manual (IBM Form. No. SA22-7204)
442 3. https://en.wikipedia.org/wiki/Channel_I/O