patch-2.3.48 linux/Documentation/parport-lowlevel.txt

Next file: linux/Documentation/pci.txt
Previous file: linux/Documentation/networking/wavelan.txt
Back to the patch index
Back to the overall index

diff -u --recursive --new-file v2.3.47/linux/Documentation/parport-lowlevel.txt linux/Documentation/parport-lowlevel.txt
@@ -0,0 +1,1490 @@
+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
FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)