s390/docs: mention subchannel types
Since the original inception of the s390-drivers document, the common I/O layer has grown support for more types of subchannels. Give at least a pointer for the various types. Signed-off-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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@ -22,9 +22,28 @@ 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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The s390 common I/O layer also provides access to some devices that are
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not strictly considered I/O devices. They are considered here as well,
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although they are not the focus 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 css bus
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===========
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The css bus contains the subchannels available on the system. They fall
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into several categories:
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* Standard I/O subchannels, for use by the system. They have a child
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device on the ccw bus and are described below.
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* I/O subchannels bound to the vfio-ccw driver. See
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Documentation/s390/vfio-ccw.txt.
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* Message subchannels. No Linux driver currently exists.
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* CHSC subchannels (at most one). The chsc subchannel driver can be used
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to send asynchronous chsc commands.
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* eADM subchannels. Used for talking to storage class memory.
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The ccw bus
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===========
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