PARPORT_YIELD(9) Parallel Port Devices PARPORT_YIELD(9)NAME
parport_yield - relinquish a parallel port temporarily
SYNOPSIS
int parport_yield(struct pardevice * dev);
ARGUMENTS
dev
a device on the parallel port
DESCRIPTION
This function relinquishes the port if it would be helpful to other drivers to do so. Afterwards it tries to reclaim the port using
parport_claim, and the return value is the same as for parport_claim. If it fails, the port is left unclaimed and it is the driver's
responsibility to reclaim the port.
The parport_yield and parport_yield_blocking functions are for marking points in the driver at which other drivers may claim the port and
use their devices. Yielding the port is similar to releasing it and reclaiming it, but is more efficient because no action is taken if
there are no other devices needing the port. In fact, nothing is done even if there are other devices waiting but the current device is
still within its "timeslice". The default timeslice is half a second, but it can be adjusted via the /proc interface.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 PARPORT_YIELD(9)
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PARPORT_REGISTER_DEV(9) Parallel Port Devices PARPORT_REGISTER_DEV(9)NAME
parport_register_device - register a device on a parallel port
SYNOPSIS
struct pardevice * parport_register_device(struct parport * port, const char * name, int (*pf) (void *), void (*kf) (void *),
void (*irq_func) (void *), int flags, void * handle);
ARGUMENTS
port
port to which the device is attached
name
a name to refer to the device
pf
preemption callback
kf
kick callback (wake-up)
irq_func
interrupt handler
flags
registration flags
handle
data for callback functions
DESCRIPTION
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.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 PARPORT_REGISTER_DEV(9)