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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 

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 

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 

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 

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 

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 

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 

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 

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 

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

      1  timed out while waiting (35ms elapsed)

SEE ALSO

parport_poll_peripheral

parport_poll_peripheral - wait for status lines, in usec

-----------------------

SYNOPSIS

#include 

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

      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 

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  error (exit as soon as possible)

     >0  timed out

parport_negotiate - perform IEEE 1284 negotiation

-----------------

SYNOPSIS

#include 

int parport_negotiate (struct parport *, int mode);

DESCRIPTION

Perform IEEE 1284 negotiation.

RETURN VALUE

    -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 

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 

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 

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 

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 

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 

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

------------------

SYNOPSIS

#include 

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 

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 

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