1=================================== 2Writing s390 channel device drivers 3=================================== 4 5:Author: Cornelia Huck 6 7Introduction 8============ 9 10This document describes the interfaces available for device drivers that 11drive s390 based channel attached I/O devices. This includes interfaces 12for interaction with the hardware and interfaces for interacting with 13the common driver core. Those interfaces are provided by the s390 common 14I/O layer. 15 16The document assumes a familarity with the technical terms associated 17with the s390 channel I/O architecture. For a description of this 18architecture, please refer to the "z/Architecture: Principles of 19Operation", IBM publication no. SA22-7832. 20 21While most I/O devices on a s390 system are typically driven through the 22channel I/O mechanism described here, there are various other methods 23(like the diag interface). These are out of the scope of this document. 24 25Some additional information can also be found in the kernel source under 26Documentation/s390/driver-model.txt. 27 28The ccw bus 29=========== 30 31The ccw bus typically contains the majority of devices available to a 32s390 system. Named after the channel command word (ccw), the basic 33command structure used to address its devices, the ccw bus contains 34so-called channel attached devices. They are addressed via I/O 35subchannels, visible on the css bus. A device driver for 36channel-attached devices, however, will never interact with the 37subchannel directly, but only via the I/O device on the ccw bus, the ccw 38device. 39 40I/O functions for channel-attached devices 41------------------------------------------ 42 43Some hardware structures have been translated into C structures for use 44by the common I/O layer and device drivers. For more information on the 45hardware structures represented here, please consult the Principles of 46Operation. 47 48.. kernel-doc:: arch/s390/include/asm/cio.h 49 :internal: 50 51ccw devices 52----------- 53 54Devices that want to initiate channel I/O need to attach to the ccw bus. 55Interaction with the driver core is done via the common I/O layer, which 56provides the abstractions of ccw devices and ccw device drivers. 57 58The functions that initiate or terminate channel I/O all act upon a ccw 59device structure. Device drivers must not bypass those functions or 60strange side effects may happen. 61 62.. kernel-doc:: arch/s390/include/asm/ccwdev.h 63 :internal: 64 65.. kernel-doc:: drivers/s390/cio/device.c 66 :export: 67 68.. kernel-doc:: drivers/s390/cio/device_ops.c 69 :export: 70 71The channel-measurement facility 72-------------------------------- 73 74The channel-measurement facility provides a means to collect measurement 75data which is made available by the channel subsystem for each channel 76attached device. 77 78.. kernel-doc:: arch/s390/include/asm/cmb.h 79 :internal: 80 81.. kernel-doc:: drivers/s390/cio/cmf.c 82 :export: 83 84The ccwgroup bus 85================ 86 87The ccwgroup bus only contains artificial devices, created by the user. 88Many networking devices (e.g. qeth) are in fact composed of several ccw 89devices (like read, write and data channel for qeth). The ccwgroup bus 90provides a mechanism to create a meta-device which contains those ccw 91devices as slave devices and can be associated with the netdevice. 92 93ccw group devices 94----------------- 95 96.. kernel-doc:: arch/s390/include/asm/ccwgroup.h 97 :internal: 98 99.. kernel-doc:: drivers/s390/cio/ccwgroup.c 100 :export: 101 102Generic interfaces 103================== 104 105Some interfaces are available to other drivers that do not necessarily 106have anything to do with the busses described above, but still are 107indirectly using basic infrastructure in the common I/O layer. One 108example is the support for adapter interrupts. 109 110.. kernel-doc:: drivers/s390/cio/airq.c 111 :export: 112