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    Cornelia

    Huck

       cornelia.huck@de.ibm.com

   2007

   IBM Corp.

     This documentation is free software; you can redistribute

     it and/or modify it under the terms of the GNU General Public

     License as published by the Free Software Foundation; either

     version 2 of the License, or (at your option) any later

     version.

     This program is distributed in the hope that it will be

     useful, but WITHOUT ANY WARRANTY; without even the implied

     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

     See the GNU General Public License for more details.

     You should have received a copy of the GNU General Public

     License along with this program; if not, write to the Free

     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,

     MA 02111-1307 USA

     For more details see the file COPYING in the source

     distribution of Linux.

    This document describes the interfaces available for device drivers that

    drive s390 based channel attached devices. This includes interfaces for

    interaction with the hardware and interfaces for interacting with the

    common driver core. Those interfaces are provided by the s390 common I/O

    layer.

    The document assumes a familarity with the technical terms associated

    with the s390 channel I/O architecture. For a description of this

    architecture, please refer to the "z/Architecture: Principles of

    Operation", IBM publication no. SA22-7832.

    While most I/O devices on a s390 system are typically driven through the

    channel I/O mechanism described here, there are various other methods

    (like the diag interface). These are out of the scope of this document.

    Some additional information can also be found in the kernel source

    under Documentation/s390/driver-model.txt.

        The ccw bus typically contains the majority of devices available to

        a s390 system. Named after the channel command word (ccw), the basic

        command structure used to address its devices, the ccw bus contains

        so-called channel attached devices. They are addressed via subchannels,

        visible on the css bus. A device driver, however, will never interact

        with the subchannel directly, but only via the device on the ccw bus,

        the ccw device.

      Some hardware structures have been translated into C structures for use

      by the common I/O layer and device drivers. For more information on

      the hardware structures represented here, please consult the Principles

      of Operation.

!Iinclude/asm-s390/cio.h

      Devices that want to initiate channel I/O need to attach to the ccw bus.

      Interaction with the driver core is done via the common I/O layer, which

      provides the abstractions of ccw devices and ccw device drivers.

      The functions that initiate or terminate channel I/O all act upon a

      ccw device structure. Device drivers must not bypass those functions

      or strange side effects may happen.

!Iinclude/asm-s390/ccwdev.h

!Edrivers/s390/cio/device.c

!Edrivers/s390/cio/device_ops.c

        The channel-measurement facility provides a means to collect

        measurement data which is made available by the channel subsystem

        for each channel attached device.

!Iinclude/asm-s390/cmb.h

!Edrivers/s390/cio/cmf.c

        The ccwgroup bus only contains artificial devices, created by the user.

        Many networking devices (e.g. qeth) are in fact composed of several

        ccw devices (like read, write and data channel for qeth). The

        ccwgroup bus provides a mechanism to create a meta-device which

        contains those ccw devices as slave devices and can be associated

        with the netdevice.

!Iinclude/asm-s390/ccwgroup.h

!Edrivers/s390/cio/ccwgroup.c