112 lines
3.6 KiB
ReStructuredText
112 lines
3.6 KiB
ReStructuredText
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Writing s390 channel device drivers
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===================================
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:Author: Cornelia Huck
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Introduction
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============
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This document describes the interfaces available for device drivers that
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drive s390 based channel attached I/O devices. This includes interfaces
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for interaction with the hardware and interfaces for interacting with
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the common driver core. Those interfaces are provided by the s390 common
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I/O layer.
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The document assumes a familarity with the technical terms associated
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with the s390 channel I/O architecture. For a description of this
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architecture, please refer to the "z/Architecture: Principles of
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Operation", IBM publication no. SA22-7832.
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While most I/O devices on a s390 system are typically driven through the
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channel I/O mechanism described here, there are various other methods
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(like the diag interface). These are out of the scope of this document.
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Some additional information can also be found in the kernel source under
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Documentation/s390/driver-model.txt.
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The ccw bus
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===========
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The ccw bus typically contains the majority of devices available to a
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s390 system. Named after the channel command word (ccw), the basic
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command structure used to address its devices, the ccw bus contains
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so-called channel attached devices. They are addressed via I/O
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subchannels, visible on the css bus. A device driver for
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channel-attached devices, however, will never interact with the
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subchannel directly, but only via the I/O device on the ccw bus, the ccw
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device.
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I/O functions for channel-attached devices
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------------------------------------------
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Some hardware structures have been translated into C structures for use
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by the common I/O layer and device drivers. For more information on the
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hardware structures represented here, please consult the Principles of
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Operation.
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.. kernel-doc:: arch/s390/include/asm/cio.h
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:internal:
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ccw devices
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-----------
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Devices that want to initiate channel I/O need to attach to the ccw bus.
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Interaction with the driver core is done via the common I/O layer, which
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provides the abstractions of ccw devices and ccw device drivers.
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The functions that initiate or terminate channel I/O all act upon a ccw
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device structure. Device drivers must not bypass those functions or
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strange side effects may happen.
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.. kernel-doc:: arch/s390/include/asm/ccwdev.h
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:internal:
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.. kernel-doc:: drivers/s390/cio/device.c
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:export:
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.. kernel-doc:: drivers/s390/cio/device_ops.c
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:export:
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The channel-measurement facility
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--------------------------------
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The channel-measurement facility provides a means to collect measurement
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data which is made available by the channel subsystem for each channel
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attached device.
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.. kernel-doc:: arch/s390/include/asm/cmb.h
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:internal:
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.. kernel-doc:: drivers/s390/cio/cmf.c
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:export:
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The ccwgroup bus
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================
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The ccwgroup bus only contains artificial devices, created by the user.
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Many networking devices (e.g. qeth) are in fact composed of several ccw
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devices (like read, write and data channel for qeth). The ccwgroup bus
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provides a mechanism to create a meta-device which contains those ccw
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devices as slave devices and can be associated with the netdevice.
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ccw group devices
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-----------------
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.. kernel-doc:: arch/s390/include/asm/ccwgroup.h
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:internal:
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.. kernel-doc:: drivers/s390/cio/ccwgroup.c
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:export:
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Generic interfaces
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==================
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Some interfaces are available to other drivers that do not necessarily
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have anything to do with the busses described above, but still are
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indirectly using basic infrastructure in the common I/O layer. One
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example is the support for adapter interrupts.
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.. kernel-doc:: drivers/s390/cio/airq.c
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:export:
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