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parport-lowlevel.txt
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===============================
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_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.
The (``name``) argument is the name of the device that appears in /proc
filesystem. The string must be valid for the whole lifetime of the
device (until parport_unregister_device is called).
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_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_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_open, parport_device_id
parport_find_class - find a device by its class
-----------------------------------------------