The Linux 2.4 Parallel Port Subsystem | ||
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port to which the device is attached
a name to refer to the device
preemption callback
kick callback (wake-up)
interrupt handler
registration flags
data for callback functions
This function, called by parallel port device drivers, declares that a device is connected to a port, and tells the system all it needs to know.
The name is allocated by the caller and must not be deallocated until the caller calls parport_unregister_device for that device.
The preemption callback function, pf, is called when this
device driver has claimed access to the port but another
device driver wants to use it. It is given handle as its
parameter, and should return zero if it is willing for the
system to release the port to another driver on its behalf.
If it wants to keep control of the port it should return
non-zero, and no action will be taken. It is good manners for
the driver to try to release the port at the earliest
opportunity after its preemption callback rejects a preemption
attempt. Note that if a preemption callback is happy for
preemption to go ahead, there is no need to release the port;
it is done automatically. This function may not block, as it
may be called from interrupt context. If the device driver
does not support preemption, pf can be NULL
.
The wake-up ("kick") callback function, kf, is called when
the port is available to be claimed for exclusive access; that
is, parport_claim is guaranteed to succeed when called from
inside the wake-up callback function. If the driver wants to
claim the port it should do so; otherwise, it need not take
any action. This function may not block, as it may be called
from interrupt context. If the device driver does not want to
be explicitly invited to claim the port in this way, kf can
be NULL
.
The interrupt handler, irq_func, is called when an interrupt arrives from the parallel port. Note that if a device driver wants to use interrupts it should use parport_enable_irq, and can also check the irq member of the parport structure representing the port.
The parallel port (lowlevel) driver is the one that has called request_irq and whose interrupt handler is called first. This handler does whatever needs to be done to the hardware to acknowledge the interrupt (for PC-style ports there is nothing special to be done). It then tells the IEEE 1284 code about the interrupt, which may involve reacting to an IEEE 1284 event depending on the current IEEE 1284 phase. After this, it calls irq_func. Needless to say, irq_func will be called from interrupt context, and may not block.
The PARPORT_DEV_EXCL
flag is for preventing port sharing, and
so should only be used when sharing the port with other device
drivers is impossible and would lead to incorrect behaviour.
Use it sparingly! Normally, flags will be zero.
This function returns a pointer to a structure that represents
the device on the port, or NULL
if there is not enough memory
to allocate space for that structure.
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