| 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'.
#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);
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.
Zero on success, otherwise an error code.
None. (Can it fail? Why return int?)
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;
}
...
}
parport_unregister_driver, parport_register_device, parport_enumerate
#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);
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.
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]);
...
}
parport_register_driver, parport_enumerate
#include <linux/parport.h> struct parport *parport_enumerate (void);
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.
A struct parport * describing a valid parallel port for the machine,
or NULL if there are none.
This function can return NULL to indicate that there are no parallel ports to use.
int detect_device (void)
{
struct parport *port;
for (port = parport_enumerate ();
port != NULL;
port = port->next) {
/* Try to detect a device on the port... */
...
}
}
...
}
parport_enumerate is deprecated; parport_register_driver should be used instead.
parport_register_driver, parport_unregister_driver
#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);
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' */
...
};
A struct pardevice *: a handle to the registered parallel port
device that can be used for parport_claim, parport_release, etc.
A return value of NULL indicates that there was a problem registering a device on that port.
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;
}
...
}
parport_unregister_device, parport_claim
SYNPOPSIS
#include <linux/parport.h> void parport_unregister_device (struct pardevice *dev);
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.
... kfree (dev->private); /* before we lose the pointer */ parport_unregister_device (dev); ...
parport_unregister_driver
#include <linux/parport.h> int parport_claim (struct pardevice *dev); int parport_claim_or_block (struct pardevice *dev);
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.
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.
| -EAGAIN | The port is unavailable at the moment, but another attempt to claim it may succeed. |
parport_release
#include <linux/parport.h> void parport_release (struct pardevice *dev);
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.
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);
...
}
change_mode, parport_claim, parport_claim_or_block, parport_yield
#include <linux/parport.h> int parport_yield (struct pardevice *dev) int parport_yield_blocking (struct pardevice *dev);
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.
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.
| -EAGAIN | Ownership of the parallel port was given away. |
parport_release
#include <linux/parport.h>
int parport_wait_peripheral (struct parport *port,
unsigned char mask,
unsigned char val);
Wait for the status lines in mask to match the values in val.
| -EINTR | a signal is pending |
| 0 | the status lines in mask have values in val |
| 1 | timed out while waiting (35ms elapsed) |
parport_poll_peripheral
#include <linux/parport.h>
int parport_poll_peripheral (struct parport *port,
unsigned char mask,
unsigned char val,
int usec);
Wait for the status lines in mask to match the values in val.
| -EINTR | a signal is pending |
| 0 | the status lines in mask have values in val |
| 1 | timed out while waiting (usec microseconds have elapsed) |
parport_wait_peripheral
#include <linux/parport.h> int parport_wait_event (struct parport *port, signed long timeout)
Wait for an event (e.g. interrupt) on a port. The timeout is in jiffies.
| 0 | success |
| <0 | error (exit as soon as possible) |
| >0 | timed out |
#include <linux/parport.h> int parport_negotiate (struct parport *, int mode);
Perform IEEE 1284 negotiation.
| 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 |
parport_read, parport_write
#include <linux/parport.h> ssize_t parport_read (struct parport *, void *buf, size_t len);
Read data from device in current IEEE 1284 transfer mode. This only works for modes that support reverse data transfer.
If negative, an error code; otherwise the number of bytes transferred.
parport_write, parport_negotiate
#include <linux/parport.h> ssize_t parport_write (struct parport *, const void *buf, size_t len);
Write data to device in current IEEE 1284 transfer mode. This only works for modes that support forward data transfer.
If negative, an error code; otherwise the number of bytes transferred.
parport_read, parport_negotiate
#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);
This is like parport_register_device but takes a device number instead of a pointer to a struct parport.
See parport_register_device. If no device is associated with devnum, NULL is returned.
parport_register_device
#include <linux/parport.h> void parport_close (struct pardevice *dev);
This is the equivalent of parport_unregister_device for parport_open.
parport_unregister_device, parport_open
#include <linux/parport.h> ssize_t parport_device_id (int devnum, char *buffer, size_t len);
Obtains the IEEE 1284 Device ID associated with a given device.
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;
Many devices have ill-formed IEEE 1284 Device IDs.
parport_find_class, parport_find_device
#include <linux/parport.h>
int parport_device_coords (int devnum, int *parport, int *mux,
int *daisy);
Convert between device number (zero-based) and device coordinates (port, multiplexor, daisy chain address).
Zero on success, in which case the coordinates are (*parport, *mux,
*daisy).
parport_open, parport_device_id
#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);
Find a device by class. The search starts from device number from+1.
The device number of the next device in that class, or -1 if no such device exists.
Example usage:
int devnum = -1;
while ((devnum = parport_find_class (PARPORT_CLASS_DIGCAM, devnum)) != -1) {
struct pardevice *dev = parport_open (devnum, ...);
...
}
parport_find_device, parport_open, parport_device_id
#include <linux/parport.h> int parport_find_device (const char *mfg, const char *mdl, int from);
Find a device by vendor and model. The search starts from device number from+1.
The device number of the next device matching the specifications, or -1 if no such device exists.
Example usage:
int devnum = -1;
while ((devnum = parport_find_device ("IOMEGA", "ZIP+", devnum)) != -1) {
struct pardevice *dev = parport_open (devnum, ...);
...
}
parport_find_class, parport_open, parport_device_id
#include <linux/parport.h> long parport_set_timeout (struct pardevice *dev, long inactivity);
Set the inactivity timeout, in jiffies, for a registered device. The previous timeout is returned.
The previous timeout, in jiffies.
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.
port->ops->xxx_read/write_yyy
The functions in the port->ops structure (struct parport_operations) are provided by the low-level driver responsible for that port.
#include <linux/parport.h>
struct parport_operations {
...
unsigned char (*read_data) (struct parport *port);
...
};
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.
write_data, read_status, write_control
#include <linux/parport.h>
struct parport_operations {
...
void (*write_data) (struct parport *port, unsigned char d);
...
};
Writes to the data register. May have side-effects (a STROBE pulse, for instance).
read_data, read_status, write_control
#include <linux/parport.h>
struct parport_operations {
...
unsigned char (*read_status) (struct parport *port);
...
};
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.
read_data, write_data, write_control
#include <linux/parport.h>
struct parport_operations {
...
unsigned char (*read_control) (struct parport *port);
...
};
Returns the last value written to the control register (either from write_control or frob_control). No port access is performed.
read_data, write_data, read_status, write_control
#include <linux/parport.h>
struct parport_operations {
...
void (*write_control) (struct parport *port, unsigned char s);
...
};
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)
read_data, write_data, read_status, frob_control
#include <linux/parport.h>
struct parport_operations {
...
unsigned char (*frob_control) (struct parport *port,
unsigned char mask,
unsigned char val);
...
};
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.
read_data, write_data, read_status, write_control
#include <linux/parport.h>
struct parport_operations {
...
void (*enable_irq) (struct parport *port);
...
};
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.
disable_irq
#include <linux/parport.h>
struct parport_operations {
...
void (*disable_irq) (struct parport *port);
...
};
The parallel port hardware is instructed not to generate interrupts. The interrupt itself is not masked.
enable_irq
#include <linux/parport.h>
struct parport_operations {
...
void (*data_forward) (struct parport *port);
...
};
Enables the data line drivers, for 8-bit host-to-peripheral communications.
data_reverse
#include <linux/parport.h>
struct parport_operations {
...
void (*data_reverse) (struct parport *port);
...
};
Places the data bus in a high impedance state, if port->modes has the PARPORT_MODE_TRISTATE bit set.
data_forward
#include <linux/parport.h>
struct parport_operations {
...
size_t (*epp_write_data) (struct parport *port, const void *buf,
size_t len, int flags);
...
};
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. |
epp_read_data, epp_write_addr, epp_read_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*epp_read_data) (struct parport *port, void *buf,
size_t len, int flags);
...
};
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. |
epp_write_data, epp_write_addr, epp_read_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*epp_write_addr) (struct parport *port,
const void *buf, size_t len, int flags);
...
};
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?)
epp_write_data, epp_read_data, epp_read_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*epp_read_addr) (struct parport *port, void *buf,
size_t len, int flags);
...
};
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?)
epp_write_data, epp_read_data, epp_write_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*ecp_write_data) (struct parport *port,
const void *buf, size_t len, int flags);
...
};
Writes a block of ECP data. The flags parameter is ignored.
The number of bytes written.
ecp_read_data, ecp_write_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*ecp_read_data) (struct parport *port,
void *buf, size_t len, int flags);
...
};
Reads a block of ECP data. The flags parameter is ignored.
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?
ecp_write_block, ecp_write_addr
#include <linux/parport.h>
struct parport_operations {
...
size_t (*ecp_write_addr) (struct parport *port,
const void *buf, size_t len, int flags);
...
};
Writes a block of ECP addresses. The flags parameter is ignored.
The number of bytes written.
This may use a FIFO, and if so shall not return until the FIFO is empty.
ecp_read_data, ecp_write_data
#include <linux/parport.h>
struct parport_operations {
...
size_t (*nibble_read_data) (struct parport *port,
void *buf, size_t len, int flags);
...
};
Reads a block of data in nibble mode. The flags parameter is ignored.
The number of whole bytes read.
byte_read_data, compat_write_data
#include <linux/parport.h>
struct parport_operations {
...
size_t (*byte_read_data) (struct parport *port,
void *buf, size_t len, int flags);
...
};
Reads a block of data in byte mode. The flags parameter is ignored.
The number of bytes read.
nibble_read_data, compat_write_data
#include <linux/parport.h>
struct parport_operations {
...
size_t (*compat_write_data) (struct parport *port,
const void *buf, size_t len, int flags);
...
};
Writes a block of data in compatibility mode. The flags parameter
is ignored.
The number of bytes written.
nibble_read_data, byte_read_data