1 =================================== 2 Writing s390 channel device drivers 3 =================================== 4 5 :Author: Cornelia Huck 6 7 Introduction 8 ============ 9 10 This document describes the interfaces available for device drivers that 11 drive s390 based channel attached I/O devices. This includes interfaces 12 for interaction with the hardware and interfaces for interacting with 13 the common driver core. Those interfaces are provided by the s390 common 14 I/O layer. 15 16 The document assumes a familarity with the technical terms associated 17 with the s390 channel I/O architecture. For a description of this 18 architecture, please refer to the "z/Architecture: Principles of 19 Operation", IBM publication no. SA22-7832. 20 21 While most I/O devices on a s390 system are typically driven through the 22 channel 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 25 The s390 common I/O layer also provides access to some devices that are 26 not strictly considered I/O devices. They are considered here as well, 27 although they are not the focus of this document. 28 29 Some additional information can also be found in the kernel source under 30 Documentation/arch/s390/driver-model.rst. 31 32 The css bus 33 =========== 34 35 The css bus contains the subchannels available on the system. They fall 36 into several categories: 37 38 * Standard I/O subchannels, for use by the system. They have a child 39 device on the ccw bus and are described below. 40 * I/O subchannels bound to the vfio-ccw driver. See 41 Documentation/arch/s390/vfio-ccw.rst. 42 * Message subchannels. No Linux driver currently exists. 43 * CHSC subchannels (at most one). The chsc subchannel driver can be used 44 to send asynchronous chsc commands. 45 * eADM subchannels. Used for talking to storage class memory. 46 47 The ccw bus 48 =========== 49 50 The ccw bus typically contains the majority of devices available to a 51 s390 system. Named after the channel command word (ccw), the basic 52 command structure used to address its devices, the ccw bus contains 53 so-called channel attached devices. They are addressed via I/O 54 subchannels, visible on the css bus. A device driver for 55 channel-attached devices, however, will never interact with the 56 subchannel directly, but only via the I/O device on the ccw bus, the ccw 57 device. 58 59 I/O functions for channel-attached devices 60 ------------------------------------------ 61 62 Some hardware structures have been translated into C structures for use 63 by the common I/O layer and device drivers. For more information on the 64 hardware structures represented here, please consult the Principles of 65 Operation. 66 67 .. kernel-doc:: arch/s390/include/asm/cio.h 68 :internal: 69 70 ccw devices 71 ----------- 72 73 Devices that want to initiate channel I/O need to attach to the ccw bus. 74 Interaction with the driver core is done via the common I/O layer, which 75 provides the abstractions of ccw devices and ccw device drivers. 76 77 The functions that initiate or terminate channel I/O all act upon a ccw 78 device structure. Device drivers must not bypass those functions or 79 strange side effects may happen. 80 81 .. kernel-doc:: arch/s390/include/asm/ccwdev.h 82 :internal: 83 84 .. kernel-doc:: drivers/s390/cio/device.c 85 :export: 86 87 .. kernel-doc:: drivers/s390/cio/device_ops.c 88 :export: 89 90 The channel-measurement facility 91 -------------------------------- 92 93 The channel-measurement facility provides a means to collect measurement 94 data which is made available by the channel subsystem for each channel 95 attached device. 96 97 .. kernel-doc:: arch/s390/include/uapi/asm/cmb.h 98 :internal: 99 100 .. kernel-doc:: drivers/s390/cio/cmf.c 101 :export: 102 103 The ccwgroup bus 104 ================ 105 106 The ccwgroup bus only contains artificial devices, created by the user. 107 Many networking devices (e.g. qeth) are in fact composed of several ccw 108 devices (like read, write and data channel for qeth). The ccwgroup bus 109 provides a mechanism to create a meta-device which contains those ccw 110 devices as slave devices and can be associated with the netdevice. 111 112 ccw group devices 113 ----------------- 114 115 .. kernel-doc:: arch/s390/include/asm/ccwgroup.h 116 :internal: 117 118 .. kernel-doc:: drivers/s390/cio/ccwgroup.c 119 :export: 120 121 Generic interfaces 122 ================== 123 124 The following section contains interfaces in use not only by drivers 125 dealing with ccw devices, but drivers for various other s390 hardware 126 as well. 127 128 Adapter interrupts 129 ------------------ 130 131 The common I/O layer provides helper functions for dealing with adapter 132 interrupts and interrupt vectors. 133 134 .. kernel-doc:: drivers/s390/cio/airq.c 135 :export:
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