Linux for S/390 and zSeries
  
  Common Device Support (CDS)
  Device Driver I/O Support Routines
  
  Authors : Ingo Adlung
  	  Cornelia Huck
  
  Copyright, IBM Corp. 1999-2002
  
  Introduction
  
  This document describes the common device support routines for Linux/390.
  Different than other hardware architectures, ESA/390 has defined a unified
  I/O access method. This gives relief to the device drivers as they don't
  have to deal with different bus types, polling versus interrupt
  processing, shared versus non-shared interrupt processing, DMA versus port
  I/O (PIO), and other hardware features more. However, this implies that
  either every single device driver needs to implement the hardware I/O
  attachment functionality itself, or the operating system provides for a
  unified method to access the hardware, providing all the functionality that
  every single device driver would have to provide itself.
  
  The document does not intend to explain the ESA/390 hardware architecture in
  every detail.This information can be obtained from the ESA/390 Principles of
  Operation manual (IBM Form. No. SA22-7201).
  
  In order to build common device support for ESA/390 I/O interfaces, a
  functional layer was introduced that provides generic I/O access methods to
  the hardware. 
  
  The common device support layer comprises the I/O support routines defined 
  below. Some of them implement common Linux device driver interfaces, while 
  some of them are ESA/390 platform specific.
  
  Note:
  In order to write a driver for S/390, you also need to look into the interface
  described in Documentation/s390/driver-model.txt.
  
  Note for porting drivers from 2.4:
  The major changes are:
  * The functions use a ccw_device instead of an irq (subchannel).
  * All drivers must define a ccw_driver (see driver-model.txt) and the associated
    functions.
  * request_irq() and free_irq() are no longer done by the driver.
  * The oper_handler is (kindof) replaced by the probe() and set_online() functions
    of the ccw_driver.
  * The not_oper_handler is (kindof) replaced by the remove() and set_offline()
    functions of the ccw_driver.
  * The channel device layer is gone.
  * The interrupt handlers must be adapted to use a ccw_device as argument.
    Moreover, they don't return a devstat, but an irb.
  * Before initiating an io, the options must be set via ccw_device_set_options().
  * Instead of calling read_dev_chars()/read_conf_data(), the driver issues
    the channel program and handles the interrupt itself.
  
  ccw_device_get_ciw()
     get commands from extended sense data.
  
  ccw_device_start()	
  ccw_device_start_timeout()
  ccw_device_start_key()
  ccw_device_start_key_timeout()
     initiate an I/O request.
  
  ccw_device_resume()
     resume channel program execution.
  
  ccw_device_halt()	
     terminate the current I/O request processed on the device.
  
  do_IRQ()	
     generic interrupt routine. This function is called by the interrupt entry
     routine whenever an I/O interrupt is presented to the system. The do_IRQ()
     routine determines the interrupt status and calls the device specific
     interrupt handler according to the rules (flags) defined during I/O request
     initiation with do_IO().
  
  The next chapters describe the functions other than do_IRQ() in more details.
  The do_IRQ() interface is not described, as it is called from the Linux/390
  first level interrupt handler only and does not comprise a device driver
  callable interface. Instead, the functional description of do_IO() also
  describes the input to the device specific interrupt handler.
  
  Note: All explanations apply also to the 64 bit architecture s390x.
  
  
  Common Device Support (CDS) for Linux/390 Device Drivers
  
  General Information
  
  The following chapters describe the I/O related interface routines the
  Linux/390 common device support (CDS) provides to allow for device specific
  driver implementations on the IBM ESA/390 hardware platform. Those interfaces
  intend to provide the functionality required by every device driver
  implementation to allow to drive a specific hardware device on the ESA/390
  platform. Some of the interface routines are specific to Linux/390 and some
  of them can be found on other Linux platforms implementations too.
  Miscellaneous function prototypes, data declarations, and macro definitions
  can be found in the architecture specific C header file
  linux/arch/s390/include/asm/irq.h.
  
  Overview of CDS interface concepts
  
  Different to other hardware platforms, the ESA/390 architecture doesn't define
  interrupt lines managed by a specific interrupt controller and bus systems
  that may or may not allow for shared interrupts, DMA processing, etc.. Instead,
  the ESA/390 architecture has implemented a so called channel subsystem, that
  provides a unified view of the devices physically attached to the systems.
  Though the ESA/390 hardware platform knows about a huge variety of different
  peripheral attachments like disk devices (aka. DASDs), tapes, communication
  controllers, etc. they can all be accessed by a well defined access method and
  they are presenting I/O completion a unified way : I/O interruptions. Every
  single device is uniquely identified to the system by a so called subchannel,
  where the ESA/390 architecture allows for 64k devices be attached.
  
  Linux, however, was first built on the Intel PC architecture, with its two
  cascaded 8259 programmable interrupt controllers (PICs), that allow for a
  maximum of 15 different interrupt lines. All devices attached to such a system
  share those 15 interrupt levels. Devices attached to the ISA bus system must
  not share interrupt levels (aka. IRQs), as the ISA bus bases on edge triggered
  interrupts. MCA, EISA, PCI and other bus systems base on level triggered
  interrupts, and therewith allow for shared IRQs. However, if multiple devices
  present their hardware status by the same (shared) IRQ, the operating system
  has to call every single device driver registered on this IRQ in order to
  determine the device driver owning the device that raised the interrupt.
  
  Up to kernel 2.4, Linux/390 used to provide interfaces via the IRQ (subchannel).
  For internal use of the common I/O layer, these are still there. However, 
  device drivers should use the new calling interface via the ccw_device only.
  
  During its startup the Linux/390 system checks for peripheral devices. Each
  of those devices is uniquely defined by a so called subchannel by the ESA/390
  channel subsystem. While the subchannel numbers are system generated, each
  subchannel also takes a user defined attribute, the so called device number.
  Both subchannel number and device number cannot exceed 65535. During sysfs
  initialisation, the information about control unit type and device types that 
  imply specific I/O commands (channel command words - CCWs) in order to operate
  the device are gathered. Device drivers can retrieve this set of hardware
  information during their initialization step to recognize the devices they
  support using the information saved in the struct ccw_device given to them.
  This methods implies that Linux/390 doesn't require to probe for free (not
  armed) interrupt request lines (IRQs) to drive its devices with. Where
  applicable, the device drivers can use issue the READ DEVICE CHARACTERISTICS
  ccw to retrieve device characteristics in its online routine.
  
  In order to allow for easy I/O initiation the CDS layer provides a
  ccw_device_start() interface that takes a device specific channel program (one
  or more CCWs) as input sets up the required architecture specific control blocks
  and initiates an I/O request on behalf of the device driver. The
  ccw_device_start() routine allows to specify whether it expects the CDS layer
  to notify the device driver for every interrupt it observes, or with final status
  only. See ccw_device_start() for more details. A device driver must never issue
  ESA/390 I/O commands itself, but must use the Linux/390 CDS interfaces instead.
  
  For long running I/O request to be canceled, the CDS layer provides the
  ccw_device_halt() function. Some devices require to initially issue a HALT
  SUBCHANNEL (HSCH) command without having pending I/O requests. This function is
  also covered by ccw_device_halt().
  
  
  get_ciw() - get command information word
  
  This call enables a device driver to get information about supported commands
  from the extended SenseID data.
  
  struct ciw *
  ccw_device_get_ciw(struct ccw_device *cdev, __u32 cmd);
  
  cdev - The ccw_device for which the command is to be retrieved.
  cmd  - The command type to be retrieved.
  
  ccw_device_get_ciw() returns:
  NULL    - No extended data available, invalid device or command not found.
  !NULL   - The command requested.
  
  
  ccw_device_start() - Initiate I/O Request
  
  The ccw_device_start() routines is the I/O request front-end processor. All
  device driver I/O requests must be issued using this routine. A device driver
  must not issue ESA/390 I/O commands itself. Instead the ccw_device_start()
  routine provides all interfaces required to drive arbitrary devices.
  
  This description also covers the status information passed to the device
  driver's interrupt handler as this is related to the rules (flags) defined
  with the associated I/O request when calling ccw_device_start().
  
  int ccw_device_start(struct ccw_device *cdev,
  		     struct ccw1 *cpa,
  		     unsigned long intparm,
  		     __u8 lpm,
  		     unsigned long flags);
  int ccw_device_start_timeout(struct ccw_device *cdev,
  			     struct ccw1 *cpa,
  			     unsigned long intparm,
  			     __u8 lpm,
  			     unsigned long flags,
  			     int expires);
  int ccw_device_start_key(struct ccw_device *cdev,
  			 struct ccw1 *cpa,
  			 unsigned long intparm,
  			 __u8 lpm,
  			 __u8 key,
  			 unsigned long flags);
  int ccw_device_start_key_timeout(struct ccw_device *cdev,
  				 struct ccw1 *cpa,
  				 unsigned long intparm,
  				 __u8 lpm,
  				 __u8 key,
  				 unsigned long flags,
  				 int expires);
  
  cdev         : ccw_device the I/O is destined for
  cpa          : logical start address of channel program
  user_intparm : user specific interrupt information; will be presented
  	       back to the device driver's interrupt handler. Allows a
                 device driver to associate the interrupt with a
                 particular I/O request.
  lpm          : defines the channel path to be used for a specific I/O
                 request. A value of 0 will make cio use the opm.
  key	     : the storage key to use for the I/O (useful for operating on a
  	       storage with a storage key != default key)
  flag         : defines the action to be performed for I/O processing
  expires      : timeout value in jiffies. The common I/O layer will terminate
  	       the running program after this and call the interrupt handler
  	       with ERR_PTR(-ETIMEDOUT) as irb.
  
  Possible flag values are :
  
  DOIO_ALLOW_SUSPEND       - channel program may become suspended
  DOIO_DENY_PREFETCH       - don't allow for CCW prefetch; usually
                             this implies the channel program might
                             become modified
  DOIO_SUPPRESS_INTER     - don't call the handler on intermediate status
  
  The cpa parameter points to the first format 1 CCW of a channel program :
  
  struct ccw1 {
        __u8  cmd_code;/* command code */
        __u8  flags;   /* flags, like IDA addressing, etc. */
        __u16 count;   /* byte count */
        __u32 cda;     /* data address */
  } __attribute__ ((packed,aligned(8)));
  
  with the following CCW flags values defined :
  
  CCW_FLAG_DC        - data chaining
  CCW_FLAG_CC        - command chaining
  CCW_FLAG_SLI       - suppress incorrect length
  CCW_FLAG_SKIP      - skip
  CCW_FLAG_PCI       - PCI
  CCW_FLAG_IDA       - indirect addressing
  CCW_FLAG_SUSPEND   - suspend
  
  
  Via ccw_device_set_options(), the device driver may specify the following
  options for the device:
  
  DOIO_EARLY_NOTIFICATION  - allow for early interrupt notification
  DOIO_REPORT_ALL          - report all interrupt conditions
  
  
  The ccw_device_start() function returns :
  
        0 - successful completion or request successfully initiated
  -EBUSY	- The device is currently processing a previous I/O request, or there is
            a status pending at the device.
  -ENODEV - cdev is invalid, the device is not operational or the ccw_device is
            not online.
  
  When the I/O request completes, the CDS first level interrupt handler will
  accumulate the status in a struct irb and then call the device interrupt handler.
  The intparm field will contain the value the device driver has associated with a 
  particular I/O request. If a pending device status was recognized, 
  intparm will be set to 0 (zero). This may happen during I/O initiation or delayed
  by an alert status notification. In any case this status is not related to the
  current (last) I/O request. In case of a delayed status notification no special
  interrupt will be presented to indicate I/O completion as the I/O request was
  never started, even though ccw_device_start() returned with successful completion.
  
  The irb may contain an error value, and the device driver should check for this
  first:
  
  -ETIMEDOUT: the common I/O layer terminated the request after the specified
              timeout value
  -EIO:       the common I/O layer terminated the request due to an error state
  
  If the concurrent sense flag in the extended status word (esw) in the irb is
  set, the field erw.scnt in the esw describes the number of device specific
  sense bytes available in the extended control word irb->scsw.ecw[]. No device
  sensing by the device driver itself is required.
  
  The device interrupt handler can use the following definitions to investigate
  the primary unit check source coded in sense byte 0 :
  
  SNS0_CMD_REJECT         0x80
  SNS0_INTERVENTION_REQ   0x40
  SNS0_BUS_OUT_CHECK      0x20
  SNS0_EQUIPMENT_CHECK    0x10
  SNS0_DATA_CHECK         0x08
  SNS0_OVERRUN            0x04
  SNS0_INCOMPL_DOMAIN     0x01
  
  Depending on the device status, multiple of those values may be set together.
  Please refer to the device specific documentation for details.
  
  The irb->scsw.cstat field provides the (accumulated) subchannel status :
  
  SCHN_STAT_PCI            - program controlled interrupt
  SCHN_STAT_INCORR_LEN     - incorrect length
  SCHN_STAT_PROG_CHECK     - program check
  SCHN_STAT_PROT_CHECK     - protection check
  SCHN_STAT_CHN_DATA_CHK   - channel data check
  SCHN_STAT_CHN_CTRL_CHK   - channel control check
  SCHN_STAT_INTF_CTRL_CHK  - interface control check
  SCHN_STAT_CHAIN_CHECK    - chaining check
  
  The irb->scsw.dstat field provides the (accumulated) device status :
  
  DEV_STAT_ATTENTION   - attention
  DEV_STAT_STAT_MOD    - status modifier
  DEV_STAT_CU_END      - control unit end
  DEV_STAT_BUSY        - busy
  DEV_STAT_CHN_END     - channel end
  DEV_STAT_DEV_END     - device end
  DEV_STAT_UNIT_CHECK  - unit check
  DEV_STAT_UNIT_EXCEP  - unit exception
  
  Please see the ESA/390 Principles of Operation manual for details on the
  individual flag meanings.
  
  Usage Notes :
  
  ccw_device_start() must be called disabled and with the ccw device lock held.
  
  The device driver is allowed to issue the next ccw_device_start() call from
  within its interrupt handler already. It is not required to schedule a
  bottom-half, unless a non deterministically long running error recovery procedure
  or similar needs to be scheduled. During I/O processing the Linux/390 generic
  I/O device driver support has already obtained the IRQ lock, i.e. the handler
  must not try to obtain it again when calling ccw_device_start() or we end in a
  deadlock situation!
  
  If a device driver relies on an I/O request to be completed prior to start the
  next it can reduce I/O processing overhead by chaining a NoOp I/O command
  CCW_CMD_NOOP to the end of the submitted CCW chain. This will force Channel-End
  and Device-End status to be presented together, with a single interrupt.
  However, this should be used with care as it implies the channel will remain
  busy, not being able to process I/O requests for other devices on the same
  channel. Therefore e.g. read commands should never use this technique, as the
  result will be presented by a single interrupt anyway.
  
  In order to minimize I/O overhead, a device driver should use the
  DOIO_REPORT_ALL  only if the device can report intermediate interrupt
  information prior to device-end the device driver urgently relies on. In this
  case all I/O interruptions are presented to the device driver until final
  status is recognized.
  
  If a device is able to recover from asynchronously presented I/O errors, it can
  perform overlapping I/O using the DOIO_EARLY_NOTIFICATION flag. While some
  devices always report channel-end and device-end together, with a single
  interrupt, others present primary status (channel-end) when the channel is
  ready for the next I/O request and secondary status (device-end) when the data
  transmission has been completed at the device.
  
  Above flag allows to exploit this feature, e.g. for communication devices that
  can handle lost data on the network to allow for enhanced I/O processing.
  
  Unless the channel subsystem at any time presents a secondary status interrupt,
  exploiting this feature will cause only primary status interrupts to be
  presented to the device driver while overlapping I/O is performed. When a
  secondary status without error (alert status) is presented, this indicates
  successful completion for all overlapping ccw_device_start() requests that have
  been issued since the last secondary (final) status.
  
  Channel programs that intend to set the suspend flag on a channel command word 
  (CCW)  must start the I/O operation with the DOIO_ALLOW_SUSPEND option or the 
  suspend flag will cause a channel program check. At the time the channel program 
  becomes suspended an intermediate interrupt will be generated by the channel 
  subsystem.
  
  ccw_device_resume() - Resume Channel Program Execution 
  
  If a device driver chooses to suspend the current channel program execution by 
  setting the CCW suspend flag on a particular CCW, the channel program execution 
  is suspended. In order to resume channel program execution the CIO layer 
  provides the ccw_device_resume() routine. 
  
  int ccw_device_resume(struct ccw_device *cdev);
  
  cdev - ccw_device the resume operation is requested for
  
  The ccw_device_resume() function returns:
  
          0  - suspended channel program is resumed
  -EBUSY     - status pending
  -ENODEV    - cdev invalid or not-operational subchannel 
  -EINVAL    - resume function not applicable  
  -ENOTCONN  - there is no I/O request pending for completion 
  
  Usage Notes:
  Please have a look at the ccw_device_start() usage notes for more details on
  suspended channel programs.
  
  ccw_device_halt() - Halt I/O Request Processing
  
  Sometimes a device driver might need a possibility to stop the processing of
  a long-running channel program or the device might require to initially issue
  a halt subchannel (HSCH) I/O command. For those purposes the ccw_device_halt()
  command is provided.
  
  ccw_device_halt() must be called disabled and with the ccw device lock held.
  
  int ccw_device_halt(struct ccw_device *cdev,
                      unsigned long intparm);
  
  cdev    : ccw_device the halt operation is requested for
  intparm : interruption parameter; value is only used if no I/O
            is outstanding, otherwise the intparm associated with
            the I/O request is returned
  
  The ccw_device_halt() function returns :
  
        0 - request successfully initiated
  -EBUSY  - the device is currently busy, or status pending.
  -ENODEV - cdev invalid.
  -EINVAL - The device is not operational or the ccw device is not online.
  
  Usage Notes :
  
  A device driver may write a never-ending channel program by writing a channel
  program that at its end loops back to its beginning by means of a transfer in
  channel (TIC)   command (CCW_CMD_TIC). Usually this is performed by network
  device drivers by setting the PCI CCW flag (CCW_FLAG_PCI). Once this CCW is
  executed a program controlled interrupt (PCI) is generated. The device driver
  can then perform an appropriate action. Prior to interrupt of an outstanding
  read to a network device (with or without PCI flag) a ccw_device_halt()
  is required to end the pending operation.
  
  ccw_device_clear() - Terminage I/O Request Processing
  
  In order to terminate all I/O processing at the subchannel, the clear subchannel
  (CSCH) command is used. It can be issued via ccw_device_clear().
  
  ccw_device_clear() must be called disabled and with the ccw device lock held.
  
  int ccw_device_clear(struct ccw_device *cdev, unsigned long intparm);
  
  cdev:	 ccw_device the clear operation is requested for
  intparm: interruption parameter (see ccw_device_halt())
  
  The ccw_device_clear() function returns:
  
        0 - request successfully initiated
  -ENODEV - cdev invalid
  -EINVAL - The device is not operational or the ccw device is not online.
  
  Miscellaneous Support Routines
  
  This chapter describes various routines to be used in a Linux/390 device
  driver programming environment.
  
  get_ccwdev_lock()
  
  Get the address of the device specific lock. This is then used in
  spin_lock() / spin_unlock() calls.
  
  
  __u8 ccw_device_get_path_mask(struct ccw_device *cdev);
  
  Get the mask of the path currently available for cdev.