FreeBSD/Linux Kernel Cross Reference
sys/Documentation/parport-lowlevel.txt

     PARPORT interface documentation
     -------------------------------
     
     Time-stamp: <2000-02-24 13:30:20 twaugh>
     
     Described here are the following functions:
     
     Global functions:
       parport_register_driver
      parport_unregister_driver
      parport_enumerate
      parport_register_device
      parport_unregister_device
      parport_claim
      parport_claim_or_block
      parport_release
      parport_yield
      parport_yield_blocking
      parport_wait_peripheral
      parport_poll_peripheral
      parport_wait_event
      parport_negotiate
      parport_read
      parport_write
      parport_open
      parport_close
      parport_device_id
      parport_device_num
      parport_device_coords
      parport_find_class
      parport_find_device
      parport_set_timeout
    
    Port functions (can be overridden by low-level drivers):
      SPP:
        port->ops->read_data
        port->ops->write_data
        port->ops->read_status
        port->ops->read_control
        port->ops->write_control
        port->ops->frob_control
        port->ops->enable_irq
        port->ops->disable_irq
        port->ops->data_forward
        port->ops->data_reverse
    
      EPP:
        port->ops->epp_write_data
        port->ops->epp_read_data
        port->ops->epp_write_addr
        port->ops->epp_read_addr
    
      ECP:
        port->ops->ecp_write_data
        port->ops->ecp_read_data
        port->ops->ecp_write_addr
    
      Other:
        port->ops->nibble_read_data
        port->ops->byte_read_data
        port->ops->compat_write_data
    
    The parport subsystem comprises 'parport' (the core port-sharing
    code), and a variety of low-level drivers that actually do the port
    accesses.  Each low-level driver handles a particular style of port
    (PC, Amiga, and so on).
    
    The parport interface to the device driver author can be broken down
    into global functions and port functions.
    
    The global functions are mostly for communicating between the device
    driver and the parport subsystem: acquiring a list of available ports,
    claiming a port for exclusive use, and so on.  They also include
    'generic' functions for doing standard things that will work on any
    IEEE 1284-capable architecture.
    
    The port functions are provided by the low-level drivers, although the
    core parport module provides generic 'defaults' for some routines.
    The port functions can be split into three groups: SPP, EPP, and ECP.
    
    SPP (Standard Parallel Port) functions modify so-called 'SPP'
    registers: data, status, and control.  The hardware may not actually
    have registers exactly like that, but the PC does and this interface is
    modelled after common PC implementations.  Other low-level drivers may
    be able to emulate most of the functionality.
    
    EPP (Enhanced Parallel Port) functions are provided for reading and
    writing in IEEE 1284 EPP mode, and ECP (Extended Capabilities Port)
    functions are used for IEEE 1284 ECP mode. (What about BECP? Does
    anyone care?)
    
    Hardware assistance for EPP and/or ECP transfers may or may not be
    available, and if it is available it may or may not be used.  If
    hardware is not used, the transfer will be software-driven.  In order
    to cope with peripherals that only tenuously support IEEE 1284, a
    low-level driver specific function is provided, for altering 'fudge
    factors'.
    
    GLOBAL FUNCTIONS
   ----------------
   
   parport_register_driver - register a device driver with parport
   -----------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct parport_driver {
           const char *name;
           void (*attach) (struct parport *);
           void (*detach) (struct parport *);
           struct parport_driver *next;
   };
   int parport_register_driver (struct parport_driver *driver);
   
   DESCRIPTION
   
   In order to be notified about parallel ports when they are detected,
   parport_register_driver should be called.  Your driver will
   immediately be notified of all ports that have already been detected,
   and of each new port as low-level drivers are loaded.
   
   A 'struct parport_driver' contains the textual name of your driver,
   a pointer to a function to handle new ports, and a pointer to a
   function to handle ports going away due to a low-level driver
   unloading.  Ports will only be detached if they are not being used
   (i.e. there are no devices registered on them).
   
   The visible parts of the 'struct parport *' argument given to
   attach/detach are:
   
   struct parport
   {
           struct parport *next; /* next parport in list */
           const char *name;     /* port's name */
           unsigned int modes;   /* bitfield of hardware modes */
           struct parport_device_info probe_info;
                                 /* IEEE1284 info */
           int number;           /* parport index */
           struct parport_operations *ops;
           ...
   };
   
   There are other members of the structure, but they should not be
   touched.
   
   The 'modes' member summarises the capabilities of the underlying
   hardware.  It consists of flags which may be bitwise-ored together:
   
     PARPORT_MODE_PCSPP            IBM PC registers are available,
                                   i.e. functions that act on data,
                                   control and status registers are
                                   probably writing directly to the
                                   hardware.
     PARPORT_MODE_TRISTATE         The data drivers may be turned off.
                                   This allows the data lines to be used
                                   for reverse (peripheral to host)
                                   transfers.
     PARPORT_MODE_COMPAT           The hardware can assist with
                                   compatibility-mode (printer)
                                   transfers, i.e. compat_write_block.
     PARPORT_MODE_EPP              The hardware can assist with EPP
                                   transfers.
     PARPORT_MODE_ECP              The hardware can assist with ECP
                                   transfers.
     PARPORT_MODE_DMA              The hardware can use DMA, so you might
                                   want to pass ISA DMA-able memory
                                   (i.e. memory allocated using the
                                   GFP_DMA flag with kmalloc) to the
                                   low-level driver in order to take
                                   advantage of it.
   
   There may be other flags in 'modes' as well.
   
   The contents of 'modes' is advisory only.  For example, if the
   hardware is capable of DMA, and PARPORT_MODE_DMA is in 'modes', it
   doesn't necessarily mean that DMA will always be used when possible.
   Similarly, hardware that is capable of assisting ECP transfers won't
   necessarily be used.
   
   RETURN VALUE
   
   Zero on success, otherwise an error code.
   
   ERRORS
   
   None. (Can it fail? Why return int?)
   
   EXAMPLE
   
   static void lp_attach (struct parport *port)
   {
           ...
           private = kmalloc (...);
           dev[count++] = parport_register_device (...);
           ...
   }
   
   static void lp_detach (struct parport *port)
   {
           ...
   }
   
   static struct parport_driver lp_driver = {
           "lp",
           lp_attach,
           lp_detach,
           NULL /* always put NULL here */
   };
   
   int lp_init (void)
   {
           ...
           if (parport_register_driver (&lp_driver)) {
                   /* Failed; nothing we can do. */
                   return -EIO;
           }
           ...
   }
   
   SEE ALSO
   
   parport_unregister_driver, parport_register_device, parport_enumerate
   
   parport_unregister_driver - tell parport to forget about this driver
   -------------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct parport_driver {
           const char *name;
           void (*attach) (struct parport *);
           void (*detach) (struct parport *);
           struct parport_driver *next;
   };
   void parport_unregister_driver (struct parport_driver *driver);
   
   DESCRIPTION
   
   This tells parport not to notify the device driver of new ports or of
   ports going away.  Registered devices belonging to that driver are NOT
   unregistered: parport_unregister_device must be used for each one.
   
   EXAMPLE
   
   void cleanup_module (void)
   {
           ...
           /* Stop notifications. */
           parport_unregister_driver (&lp_driver);
   
           /* Unregister devices. */
           for (i = 0; i < NUM_DEVS; i++)
                   parport_unregister_device (dev[i]);
           ...
   }
   
   SEE ALSO
   
   parport_register_driver, parport_enumerate
   
   parport_enumerate - retrieve a list of parallel ports (DEPRECATED)
   -----------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct parport *parport_enumerate (void);
   
   DESCRIPTION
   
   Retrieve the first of a list of valid parallel ports for this machine.
   Successive parallel ports can be found using the 'struct parport
   *next' element of the 'struct parport *' that is returned.  If 'next'
   is NULL, there are no more parallel ports in the list.  The number of
   ports in the list will not exceed PARPORT_MAX.
   
   RETURN VALUE
   
   A 'struct parport *' describing a valid parallel port for the machine,
   or NULL if there are none.
   
   ERRORS
   
   This function can return NULL to indicate that there are no parallel
   ports to use.
   
   EXAMPLE
   
   int detect_device (void)
   {
           struct parport *port;
   
           for (port = parport_enumerate ();
                port != NULL;
                port = port->next) {
                   /* Try to detect a device on the port... */
                   ...
                }
           }
   
           ...
   }
   
   NOTES
   
   parport_enumerate is deprecated; parport_register_driver should be
   used instead.
   
   SEE ALSO
   
   parport_register_driver, parport_unregister_driver
   
   parport_register_device - register to use a port
   -----------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   typedef int (*preempt_func) (void *handle);
   typedef void (*wakeup_func) (void *handle);
   typedef int (*irq_func) (int irq, void *handle, struct pt_regs *);
   
   struct pardevice *parport_register_device(struct parport *port,
                                             const char *name,
                                             preempt_func preempt,
                                             wakeup_func wakeup,
                                             irq_func irq,
                                             int flags,
                                             void *handle);
   
   DESCRIPTION
   
   Use this function to register your device driver on a parallel port
   ('port').  Once you have done that, you will be able to use
   parport_claim and parport_release in order to use the port.
   
   This function will register three callbacks into your driver:
   'preempt', 'wakeup' and 'irq'.  Each of these may be NULL in order to
   indicate that you do not want a callback.
   
   When the 'preempt' function is called, it is because another driver
   wishes to use the parallel port.  The 'preempt' function should return
   non-zero if the parallel port cannot be released yet -- if zero is
   returned, the port is lost to another driver and the port must be
   re-claimed before use.
   
   The 'wakeup' function is called once another driver has released the
   port and no other driver has yet claimed it.  You can claim the
   parallel port from within the 'wakeup' function (in which case the
   claim is guaranteed to succeed), or choose not to if you don't need it
   now.
   
   If an interrupt occurs on the parallel port your driver has claimed,
   the 'irq' function will be called. (Write something about shared
   interrupts here.)
   
   The 'handle' is a pointer to driver-specific data, and is passed to
   the callback functions.
   
   'flags' may be a bitwise combination of the following flags:
   
           Flag            Meaning
     PARPORT_DEV_EXCL      The device cannot share the parallel port at all.
                           Use this only when absolutely necessary.
   
   The typedefs are not actually defined -- they are only shown in order
   to make the function prototype more readable.
   
   The visible parts of the returned 'struct pardevice' are:
   
   struct pardevice {
           struct parport *port;   /* Associated port */
           void *private;          /* Device driver's 'handle' */
           ...
   };
   
   RETURN VALUE
   
   A 'struct pardevice *': a handle to the registered parallel port
   device that can be used for parport_claim, parport_release, etc.
   
   ERRORS
   
   A return value of NULL indicates that there was a problem registering
   a device on that port.
   
   EXAMPLE
   
   static int preempt (void *handle)
   {
           if (busy_right_now)
                   return 1;
   
           must_reclaim_port = 1;
           return 0;
   }
   
   static void wakeup (void *handle)
   {
           struct toaster *private = handle;
           struct pardevice *dev = private->dev;
           if (!dev) return; /* avoid races */
   
           if (want_port)
                   parport_claim (dev);
   }
   
   static int toaster_detect (struct toaster *private, struct parport *port)
   {
           private->dev = parport_register_device (port, "toaster", preempt,
                                                   wakeup, NULL, 0,
                                                   private);
           if (!private->dev)
                   /* Couldn't register with parport. */
                   return -EIO;
   
           must_reclaim_port = 0;
           busy_right_now = 1;
           parport_claim_or_block (private->dev);
           ...
           /* Don't need the port while the toaster warms up. */
           busy_right_now = 0;
           ...
           busy_right_now = 1;
           if (must_reclaim_port) {
                   parport_claim_or_block (private->dev);
                   must_reclaim_port = 0;
           }
           ...
   }
   
   SEE ALSO
   
   parport_unregister_device, parport_claim
   
   parport_unregister_device - finish using a port
   -------------------------
   
   SYNPOPSIS
   
   #include <linux/parport.h>
   
   void parport_unregister_device (struct pardevice *dev);
   
   DESCRIPTION
   
   This function is the opposite of parport_register_device.  After using
   parport_unregister_device, 'dev' is no longer a valid device handle.
   
   You should not unregister a device that is currently claimed, although
   if you do it will be released automatically.
   
   EXAMPLE
   
           ...
           kfree (dev->private); /* before we lose the pointer */
           parport_unregister_device (dev);
           ...
   
   SEE ALSO
   
   parport_unregister_driver
   
   parport_claim, parport_claim_or_block - claim the parallel port for a device
   -------------------------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_claim (struct pardevice *dev);
   int parport_claim_or_block (struct pardevice *dev);
   
   DESCRIPTION
   
   These functions attempt to gain control of the parallel port on which
   'dev' is registered.  'parport_claim' does not block, but
   'parport_claim_or_block' may do. (Put something here about blocking
   interruptibly or non-interruptibly.)
   
   You should not try to claim a port that you have already claimed.
   
   RETURN VALUE
   
   A return value of zero indicates that the port was successfully
   claimed, and the caller now has possession of the parallel port.
   
   If 'parport_claim_or_block' blocks before returning successfully, the
   return value is positive.
   
   ERRORS
   
     -EAGAIN  The port is unavailable at the moment, but another attempt
              to claim it may succeed.
   
   SEE ALSO
   
   parport_release
   
   parport_release - release the parallel port
   ---------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   void parport_release (struct pardevice *dev);
   
   DESCRIPTION
   
   Once a parallel port device has been claimed, it can be released using
   'parport_release'.  It cannot fail, but you should not release a
   device that you do not have possession of.
   
   EXAMPLE
   
   static size_t write (struct pardevice *dev, const void *buf,
                        size_t len)
   {
           ...
           written = dev->port->ops->write_ecp_data (dev->port, buf,
                                                     len);
           parport_release (dev);
           ...
   }
   
   
   SEE ALSO
   
   change_mode, parport_claim, parport_claim_or_block, parport_yield
   
   parport_yield, parport_yield_blocking - temporarily release a parallel port
   -------------------------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_yield (struct pardevice *dev)
   int parport_yield_blocking (struct pardevice *dev);
   
   DESCRIPTION
   
   When a driver has control of a parallel port, it may allow another
   driver to temporarily 'borrow' it.  'parport_yield' does not block;
   'parport_yield_blocking' may do.
   
   RETURN VALUE
   
   A return value of zero indicates that the caller still owns the port
   and the call did not block.
   
   A positive return value from 'parport_yield_blocking' indicates that
   the caller still owns the port and the call blocked.
   
   A return value of -EAGAIN indicates that the caller no longer owns the
   port, and it must be re-claimed before use.
   
   ERRORS
   
     -EAGAIN  Ownership of the parallel port was given away.
   
   SEE ALSO
   
   parport_release
   
   parport_wait_peripheral - wait for status lines, up to 35ms
   -----------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_wait_peripheral (struct parport *port,
                                unsigned char mask,
                                unsigned char val);
   
   DESCRIPTION
   
   Wait for the status lines in mask to match the values in val.
   
   RETURN VALUE
   
    -EINTR  a signal is pending
         0  the status lines in mask have values in val
         1  timed out while waiting (35ms elapsed)
   
   SEE ALSO
   
   parport_poll_peripheral
   
   parport_poll_peripheral - wait for status lines, in usec
   -----------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_poll_peripheral (struct parport *port,
                                unsigned char mask,
                                unsigned char val,
                                int usec);
   
   DESCRIPTION
   
   Wait for the status lines in mask to match the values in val.
   
   RETURN VALUE
   
    -EINTR  a signal is pending
         0  the status lines in mask have values in val
         1  timed out while waiting (usec microseconds have elapsed)
   
   SEE ALSO
   
   parport_wait_peripheral
   
   parport_wait_event - wait for an event on a port
   ------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_wait_event (struct parport *port, signed long timeout)
   
   DESCRIPTION
   
   Wait for an event (e.g. interrupt) on a port.  The timeout is in
   jiffies.
   
   RETURN VALUE
   
         0  success
        <0  error (exit as soon as possible)
        >0  timed out
   
   parport_negotiate - perform IEEE 1284 negotiation
   -----------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_negotiate (struct parport *, int mode);
   
   DESCRIPTION
   
   Perform IEEE 1284 negotiation.
   
   RETURN VALUE
   
        0  handshake OK; IEEE 1284 peripheral and mode available
       -1  handshake failed; peripheral not compliant (or none present)
        1  handshake OK; IEEE 1284 peripheral present but mode not
           available
   
   SEE ALSO
   
   parport_read, parport_write
   
   parport_read - read data from device
   ------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   ssize_t parport_read (struct parport *, void *buf, size_t len);
   
   DESCRIPTION
   
   Read data from device in current IEEE 1284 transfer mode.  This only
   works for modes that support reverse data transfer.
   
   RETURN VALUE
   
   If negative, an error code; otherwise the number of bytes transferred.
   
   SEE ALSO
   
   parport_write, parport_negotiate
   
   parport_write - write data to device
   -------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   ssize_t parport_write (struct parport *, const void *buf, size_t len);
   
   DESCRIPTION
   
   Write data to device in current IEEE 1284 transfer mode.  This only
   works for modes that support forward data transfer.
   
   RETURN VALUE
   
   If negative, an error code; otherwise the number of bytes transferred.
   
   SEE ALSO
   
   parport_read, parport_negotiate
   
   parport_open - register device for particular device number
   ------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct pardevice *parport_open (int devnum, const char *name,
                                   int (*pf) (void *),
                                   void (*kf) (void *),
                                   void (*irqf) (int, void *,
                                                 struct pt_regs *),
                                   int flags, void *handle);
   
   DESCRIPTION
   
   This is like parport_register_device but takes a device number instead
   of a pointer to a struct parport.
   
   RETURN VALUE
   
   See parport_register_device.  If no device is associated with devnum,
   NULL is returned.
   
   SEE ALSO
   
   parport_register_device, parport_device_num
   
   parport_close - unregister device for particular device number
   -------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   void parport_close (struct pardevice *dev);
   
   DESCRIPTION
   
   This is the equivalent of parport_unregister_device for parport_open.
   
   SEE ALSO
   
   parport_unregister_device, parport_open
   
   parport_device_id - obtain IEEE 1284 Device ID
   -----------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   ssize_t parport_device_id (int devnum, char *buffer, size_t len);
   
   DESCRIPTION
   
   Obtains the IEEE 1284 Device ID associated with a given device.
   
   RETURN VALUE
   
   If negative, an error code; otherwise, the number of bytes of buffer
   that contain the device ID.  The format of the device ID is as
   follows:
   
   [length][ID]
   
   The first two bytes indicate the inclusive length of the entire Device
   ID, and are in big-endian order.  The ID is a sequence of pairs of the
   form:
   
   key:value;
   
   NOTES
   
   Many devices have ill-formed IEEE 1284 Device IDs.
   
   SEE ALSO
   
   parport_find_class, parport_find_device, parport_device_num
   
   parport_device_num - convert device coordinates to device number
   ------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_device_num (int parport, int mux, int daisy);
   
   DESCRIPTION
   
   Convert between device coordinates (port, multiplexor, daisy chain
   address) and device number (zero-based).
   
   RETURN VALUE
   
   Device number, or -1 if no device at given coordinates.
   
   SEE ALSO
   
   parport_device_coords, parport_open, parport_device_id
   
   parport_device_coords - convert device number to device coordinates
   ------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_device_coords (int devnum, int *parport, int *mux,
                              int *daisy);
   
   DESCRIPTION
   
   Convert between device number (zero-based) and device coordinates
   (port, multiplexor, daisy chain address).
   
   RETURN VALUE
   
   Zero on success, in which case the coordinates are (*parport, *mux,
   *daisy).
   
   SEE ALSO
   
   parport_device_num, parport_open, parport_device_id
   
   parport_find_class - find a device by its class
   ------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   typedef enum {
           PARPORT_CLASS_LEGACY = 0,       /* Non-IEEE1284 device */
           PARPORT_CLASS_PRINTER,
           PARPORT_CLASS_MODEM,
           PARPORT_CLASS_NET,
           PARPORT_CLASS_HDC,              /* Hard disk controller */
           PARPORT_CLASS_PCMCIA,
           PARPORT_CLASS_MEDIA,            /* Multimedia device */
           PARPORT_CLASS_FDC,              /* Floppy disk controller */
           PARPORT_CLASS_PORTS,
           PARPORT_CLASS_SCANNER,
           PARPORT_CLASS_DIGCAM,
           PARPORT_CLASS_OTHER,            /* Anything else */
           PARPORT_CLASS_UNSPEC,           /* No CLS field in ID */
           PARPORT_CLASS_SCSIADAPTER
   } parport_device_class;
   
   int parport_find_class (parport_device_class cls, int from);
   
   DESCRIPTION
   
   Find a device by class.  The search starts from device number from+1.
   
   RETURN VALUE
   
   The device number of the next device in that class, or -1 if no such
   device exists.
   
   NOTES
   
   Example usage:
   
   int devnum = -1;
   while ((devnum = parport_find_class (PARPORT_CLASS_DIGCAM, devnum)) != -1) {
       struct pardevice *dev = parport_open (devnum, ...);
       ...
   }
   
   SEE ALSO
   
   parport_find_device, parport_open, parport_device_id
   
   parport_find_device - find a device by its class
   ------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   int parport_find_device (const char *mfg, const char *mdl, int from);
   
   DESCRIPTION
   
   Find a device by vendor and model.  The search starts from device
   number from+1.
   
   RETURN VALUE
   
   The device number of the next device matching the specifications, or
   -1 if no such device exists.
   
   NOTES
   
   Example usage:
   
   int devnum = -1;
   while ((devnum = parport_find_device ("IOMEGA", "ZIP+", devnum)) != -1) {
       struct pardevice *dev = parport_open (devnum, ...);
       ...
   }
   
   SEE ALSO
   
   parport_find_class, parport_open, parport_device_id
   
   parport_set_timeout - set the inactivity timeout
   -------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   long parport_set_timeout (struct pardevice *dev, long inactivity);
   
   DESCRIPTION
   
   Set the inactivity timeout, in jiffies, for a registered device.  The
   previous timeout is returned.
   
   RETURN VALUE
   
   The previous timeout, in jiffies.
   
   NOTES
   
   Some of the port->ops functions for a parport may take time, owing to
   delays at the peripheral.  After the peripheral has not responded for
   'inactivity' jiffies, a timeout will occur and the blocking function
   will return.
   
   A timeout of 0 jiffies is a special case: the function must do as much
   as it can without blocking or leaving the hardware in an unknown
   state.  If port operations are performed from within an interrupt
   handler, for instance, a timeout of 0 jiffies should be used.
   
   Once set for a registered device, the timeout will remain at the set
   value until set again.
   
   SEE ALSO
   
   port->ops->xxx_read/write_yyy
   
   PORT FUNCTIONS
   --------------
   
   The functions in the port->ops structure (struct parport_operations)
   are provided by the low-level driver responsible for that port.
   
   port->ops->read_data - read the data register
   --------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct parport_operations {
           ...
           unsigned char (*read_data) (struct parport *port);
           ...
   };
   
   DESCRIPTION
   
   If port->modes contains the PARPORT_MODE_TRISTATE flag and the
   PARPORT_CONTROL_DIRECTION bit in the control register is set, this
   returns the value on the data pins.  If port->modes contains the
   PARPORT_MODE_TRISTATE flag and the PARPORT_CONTROL_DIRECTION bit is
   not set, the return value _may_ be the last value written to the data
   register.  Otherwise the return value is undefined.
   
   SEE ALSO
   
   write_data, read_status, write_control
   
   port->ops->write_data - write the data register
   ---------------------
   
   SYNOPSIS
   
   #include <linux/parport.h>
   
   struct parport_operations {
           ...
           void (*write_data) (struct parport *port, unsigned char d);
           ...
  };
  
  DESCRIPTION
  
  Writes to the data register.  May have side-effects (a STROBE pulse,
  for instance).
  
  SEE ALSO
  
  read_data, read_status, write_control
  
  port->ops->read_status - read the status register
  ----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          unsigned char (*read_status) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  Reads from the status register.  This is a bitmask:
  
  - PARPORT_STATUS_ERROR (printer fault, "nFault")
  - PARPORT_STATUS_SELECT (on-line, "Select")
  - PARPORT_STATUS_PAPEROUT (no paper, "PError")
  - PARPORT_STATUS_ACK (handshake, "nAck")
  - PARPORT_STATUS_BUSY (busy, "Busy")
  
  There may be other bits set.
  
  SEE ALSO
  
  read_data, write_data, write_control
  
  port->ops->read_control - read the control register
  -----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          unsigned char (*read_control) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  Returns the last value written to the control register (either from
  write_control or frob_control).  No port access is performed.
  
  SEE ALSO
  
  read_data, write_data, read_status, write_control
  
  port->ops->write_control - write the control register
  ------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*write_status) (struct parport *port, unsigned char s);
          ...
  };
  
  DESCRIPTION
  
  Writes to the control register. This is a bitmask:
                            _______
  - PARPORT_CONTROL_STROBE (nStrobe)
                            _______
  - PARPORT_CONTROL_AUTOFD (nAutoFd)
                          _____
  - PARPORT_CONTROL_INIT (nInit)
                            _________
  - PARPORT_CONTROL_SELECT (nSelectIn)
  
  SEE ALSO
  
  read_data, write_data, read_status, frob_control
  
  port->ops->frob_control - write control register bits
  -----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*frob_control) (struct parport *port,
                                unsigned char mask,
                                unsigned char val);
          ...
  };
  
  DESCRIPTION
  
  This is equivalent to reading from the control register, masking out
  the bits in mask, exclusive-or'ing with the bits in val, and writing
  the result to the control register.
  
  As some ports don't allow reads from the control port, a software copy
  of its contents is maintained, so frob_control is in fact only one
  port access.
  
  SEE ALSO
  
  read_data, write_data, read_status, write_control
  
  port->ops->enable_irq - enable interrupt generation
  ---------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*enable_irq) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  The parallel port hardware is instructed to generate interrupts at
  appropriate moments, although those moments are
  architecture-specific.  For the PC architecture, interrupts are
  commonly generated on the rising edge of nAck.
  
  SEE ALSO
  
  disable_irq
  
  port->ops->disable_irq - disable interrupt generation
  ----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*disable_irq) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  The parallel port hardware is instructed not to generate interrupts.
  The interrupt itself is not masked.
  
  SEE ALSO
  
  enable_irq
  
  port->ops->data_forward - enable data drivers
  -----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*data_forward) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  Enables the data line drivers, for 8-bit host-to-peripheral
  communications.
  
  SEE ALSO
  
  data_reverse
  
  port->ops->data_reverse - tristate the buffer
  -----------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          void (*data_reverse) (struct parport *port);
          ...
  };
  
  DESCRIPTION
  
  Places the data bus in a high impedance state, if port->modes has the
  PARPORT_MODE_TRISTATE bit set.
  
  SEE ALSO
  
  data_forward
  
  port->ops->epp_write_data - write EPP data
  -------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*epp_write_data) (struct parport *port, const void *buf,
                                    size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Writes data in EPP mode, and returns the number of bytes written.
  
  The 'flags' parameter may be one or more of the following,
  bitwise-or'ed together:
  
  PARPORT_EPP_FAST        Use fast transfers. Some chips provide 16-bit and
                          32-bit registers.  However, if a transfer
                          times out, the return value may be unreliable.
  
  SEE ALSO
  
  epp_read_data, epp_write_addr, epp_read_addr
  
  port->ops->epp_read_data - read EPP data
  ------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*epp_read_data) (struct parport *port, void *buf,
                                   size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Reads data in EPP mode, and returns the number of bytes read.
  
  The 'flags' parameter may be one or more of the following,
  bitwise-or'ed together:
  
  PARPORT_EPP_FAST        Use fast transfers. Some chips provide 16-bit and
                          32-bit registers.  However, if a transfer
                          times out, the return value may be unreliable.
  
  SEE ALSO
  
  epp_write_data, epp_write_addr, epp_read_addr
  
  port->ops->epp_write_addr - write EPP address
  -------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*epp_write_addr) (struct parport *port,
                                    const void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Writes EPP addresses (8 bits each), and returns the number written.
  
  The 'flags' parameter may be one or more of the following,
  bitwise-or'ed together:
  
  PARPORT_EPP_FAST        Use fast transfers. Some chips provide 16-bit and
                          32-bit registers.  However, if a transfer
                          times out, the return value may be unreliable.
  
  (Does PARPORT_EPP_FAST make sense for this function?)
  
  SEE ALSO
  
  epp_write_data, epp_read_data, epp_read_addr
  
  port->ops->epp_read_addr - read EPP address
  ------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*epp_read_addr) (struct parport *port, void *buf,
                                   size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Reads EPP addresses (8 bits each), and returns the number read.
  
  The 'flags' parameter may be one or more of the following,
  bitwise-or'ed together:
  
  PARPORT_EPP_FAST        Use fast transfers. Some chips provide 16-bit and
                          32-bit registers.  However, if a transfer
                          times out, the return value may be unreliable.
  
  (Does PARPORT_EPP_FAST make sense for this function?)
  
  SEE ALSO
  
  epp_write_data, epp_read_data, epp_write_addr
  
  port->ops->ecp_write_data - write a block of ECP data
  -------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*ecp_write_data) (struct parport *port,
                                    const void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Writes a block of ECP data.  The 'flags' parameter is ignored.
  
  RETURN VALUE
  
  The number of bytes written.
  
  SEE ALSO
  
  ecp_read_data, ecp_write_addr
  
  port->ops->ecp_read_data - read a block of ECP data
  ------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*ecp_read_data) (struct parport *port,
                                   void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Reads a block of ECP data.  The 'flags' parameter is ignored.
  
  RETURN VALUE
  
  The number of bytes read.  NB. There may be more unread data in a
  FIFO.  Is there a way of stunning the FIFO to prevent this?
  
  SEE ALSO
  
  ecp_write_block, ecp_write_addr
  
  port->ops->ecp_write_addr - write a block of ECP addresses
  -------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*ecp_write_addr) (struct parport *port,
                                    const void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Writes a block of ECP addresses.  The 'flags' parameter is ignored.
  
  RETURN VALUE
  
  The number of bytes written.
  
  NOTES
  
  This may use a FIFO, and if so shall not return until the FIFO is empty.
  
  SEE ALSO
  
  ecp_read_data, ecp_write_data
  
  port->ops->nibble_read_data - read a block of data in nibble mode
  ---------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*nibble_read_data) (struct parport *port,
                                      void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Reads a block of data in nibble mode.  The 'flags' parameter is ignored.
  
  RETURN VALUE
  
  The number of whole bytes read.
  
  SEE ALSO
  
  byte_read_data, compat_write_data
  
  port->ops->byte_read_data - read a block of data in byte mode
  -------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*byte_read_data) (struct parport *port,
                                    void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Reads a block of data in byte mode.  The 'flags' parameter is ignored.
  
  RETURN VALUE
  
  The number of bytes read.
  
  SEE ALSO
  
  nibble_read_data, compat_write_data
  
  port->ops->compat_write_data - write a block of data in compatibility mode
  ----------------------------
  
  SYNOPSIS
  
  #include <linux/parport.h>
  
  struct parport_operations {
          ...
          size_t (*compat_write_data) (struct parport *port,
                                       const void *buf, size_t len, int flags);
          ...
  };
  
  DESCRIPTION
  
  Writes a block of data in compatibility mode.  The 'flags' parameter
  is ignored.
  
  RETURN VALUE
  
  The number of bytes written.
  
  SEE ALSO
  
  nibble_read_data, byte_read_data

Cache object: 7d0dd477ed271617de5be0d46ac21c64