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The VME subsystem graduated from staging into a top-level subsystem in
2012, with commit db3b9e990e
("Staging: VME: move VME drivers out of
staging") stating:
The VME device drivers have not moved out yet due to some API
questions they are still working through, that should happen soon,
hopefully.
However, this never happened: maintenance of drivers/vme effectively
stopped in 2017, with all subsequent changes being treewide cleanups.
No hardware driver remains in staging, only the limited user-level
access, and I just removed one of the two bridge drivers and the only
remaining board.
drivers/staging/vme/devices/ was recently moved to
drivers/staging/vme_user/, but as the vme_user driver is the only one
remaining for this subsystem, it is easier to just move the remaining
three source files into this directory rather than keeping the original
hierarchy.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20220606084109.4108188-3-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
298 lines
10 KiB
ReStructuredText
298 lines
10 KiB
ReStructuredText
VME Device Drivers
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==================
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Driver registration
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-------------------
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As with other subsystems within the Linux kernel, VME device drivers register
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with the VME subsystem, typically called from the devices init routine. This is
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achieved via a call to :c:func:`vme_register_driver`.
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A pointer to a structure of type :c:type:`struct vme_driver <vme_driver>` must
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be provided to the registration function. Along with the maximum number of
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devices your driver is able to support.
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At the minimum, the '.name', '.match' and '.probe' elements of
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:c:type:`struct vme_driver <vme_driver>` should be correctly set. The '.name'
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element is a pointer to a string holding the device driver's name.
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The '.match' function allows control over which VME devices should be registered
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with the driver. The match function should return 1 if a device should be
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probed and 0 otherwise. This example match function (from vme_user.c) limits
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the number of devices probed to one:
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.. code-block:: c
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#define USER_BUS_MAX 1
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...
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static int vme_user_match(struct vme_dev *vdev)
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{
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if (vdev->id.num >= USER_BUS_MAX)
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return 0;
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return 1;
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}
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The '.probe' element should contain a pointer to the probe routine. The
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probe routine is passed a :c:type:`struct vme_dev <vme_dev>` pointer as an
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argument.
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Here, the 'num' field refers to the sequential device ID for this specific
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driver. The bridge number (or bus number) can be accessed using
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dev->bridge->num.
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A function is also provided to unregister the driver from the VME core called
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:c:func:`vme_unregister_driver` and should usually be called from the device
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driver's exit routine.
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Resource management
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-------------------
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Once a driver has registered with the VME core the provided match routine will
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be called the number of times specified during the registration. If a match
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succeeds, a non-zero value should be returned. A zero return value indicates
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failure. For all successful matches, the probe routine of the corresponding
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driver is called. The probe routine is passed a pointer to the devices
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device structure. This pointer should be saved, it will be required for
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requesting VME resources.
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The driver can request ownership of one or more master windows
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(:c:func:`vme_master_request`), slave windows (:c:func:`vme_slave_request`)
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and/or dma channels (:c:func:`vme_dma_request`). Rather than allowing the device
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driver to request a specific window or DMA channel (which may be used by a
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different driver) the API allows a resource to be assigned based on the required
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attributes of the driver in question. For slave windows these attributes are
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split into the VME address spaces that need to be accessed in 'aspace' and VME
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bus cycle types required in 'cycle'. Master windows add a further set of
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attributes in 'width' specifying the required data transfer widths. These
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attributes are defined as bitmasks and as such any combination of the
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attributes can be requested for a single window, the core will assign a window
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that meets the requirements, returning a pointer of type vme_resource that
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should be used to identify the allocated resource when it is used. For DMA
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controllers, the request function requires the potential direction of any
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transfers to be provided in the route attributes. This is typically VME-to-MEM
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and/or MEM-to-VME, though some hardware can support VME-to-VME and MEM-to-MEM
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transfers as well as test pattern generation. If an unallocated window fitting
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the requirements can not be found a NULL pointer will be returned.
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Functions are also provided to free window allocations once they are no longer
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required. These functions (:c:func:`vme_master_free`, :c:func:`vme_slave_free`
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and :c:func:`vme_dma_free`) should be passed the pointer to the resource
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provided during resource allocation.
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Master windows
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--------------
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Master windows provide access from the local processor[s] out onto the VME bus.
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The number of windows available and the available access modes is dependent on
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the underlying chipset. A window must be configured before it can be used.
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Master window configuration
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Once a master window has been assigned :c:func:`vme_master_set` can be used to
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configure it and :c:func:`vme_master_get` to retrieve the current settings. The
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address spaces, transfer widths and cycle types are the same as described
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under resource management, however some of the options are mutually exclusive.
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For example, only one address space may be specified.
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Master window access
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~~~~~~~~~~~~~~~~~~~~
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The function :c:func:`vme_master_read` can be used to read from and
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:c:func:`vme_master_write` used to write to configured master windows.
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In addition to simple reads and writes, :c:func:`vme_master_rmw` is provided to
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do a read-modify-write transaction. Parts of a VME window can also be mapped
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into user space memory using :c:func:`vme_master_mmap`.
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Slave windows
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-------------
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Slave windows provide devices on the VME bus access into mapped portions of the
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local memory. The number of windows available and the access modes that can be
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used is dependent on the underlying chipset. A window must be configured before
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it can be used.
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Slave window configuration
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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Once a slave window has been assigned :c:func:`vme_slave_set` can be used to
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configure it and :c:func:`vme_slave_get` to retrieve the current settings.
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The address spaces, transfer widths and cycle types are the same as described
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under resource management, however some of the options are mutually exclusive.
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For example, only one address space may be specified.
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Slave window buffer allocation
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Functions are provided to allow the user to allocate
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(:c:func:`vme_alloc_consistent`) and free (:c:func:`vme_free_consistent`)
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contiguous buffers which will be accessible by the VME bridge. These functions
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do not have to be used, other methods can be used to allocate a buffer, though
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care must be taken to ensure that they are contiguous and accessible by the VME
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bridge.
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Slave window access
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~~~~~~~~~~~~~~~~~~~
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Slave windows map local memory onto the VME bus, the standard methods for
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accessing memory should be used.
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DMA channels
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------------
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The VME DMA transfer provides the ability to run link-list DMA transfers. The
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API introduces the concept of DMA lists. Each DMA list is a link-list which can
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be passed to a DMA controller. Multiple lists can be created, extended,
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executed, reused and destroyed.
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List Management
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~~~~~~~~~~~~~~~
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The function :c:func:`vme_new_dma_list` is provided to create and
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:c:func:`vme_dma_list_free` to destroy DMA lists. Execution of a list will not
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automatically destroy the list, thus enabling a list to be reused for repetitive
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tasks.
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List Population
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~~~~~~~~~~~~~~~
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An item can be added to a list using :c:func:`vme_dma_list_add` (the source and
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destination attributes need to be created before calling this function, this is
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covered under "Transfer Attributes").
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.. note::
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The detailed attributes of the transfers source and destination
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are not checked until an entry is added to a DMA list, the request
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for a DMA channel purely checks the directions in which the
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controller is expected to transfer data. As a result it is
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possible for this call to return an error, for example if the
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source or destination is in an unsupported VME address space.
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Transfer Attributes
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~~~~~~~~~~~~~~~~~~~
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The attributes for the source and destination are handled separately from adding
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an item to a list. This is due to the diverse attributes required for each type
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of source and destination. There are functions to create attributes for PCI, VME
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and pattern sources and destinations (where appropriate):
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- PCI source or destination: :c:func:`vme_dma_pci_attribute`
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- VME source or destination: :c:func:`vme_dma_vme_attribute`
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- Pattern source: :c:func:`vme_dma_pattern_attribute`
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The function :c:func:`vme_dma_free_attribute` should be used to free an
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attribute.
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List Execution
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~~~~~~~~~~~~~~
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The function :c:func:`vme_dma_list_exec` queues a list for execution and will
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return once the list has been executed.
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Interrupts
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----------
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The VME API provides functions to attach and detach callbacks to specific VME
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level and status ID combinations and for the generation of VME interrupts with
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specific VME level and status IDs.
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Attaching Interrupt Handlers
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The function :c:func:`vme_irq_request` can be used to attach and
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:c:func:`vme_irq_free` to free a specific VME level and status ID combination.
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Any given combination can only be assigned a single callback function. A void
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pointer parameter is provided, the value of which is passed to the callback
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function, the use of this pointer is user undefined. The callback parameters are
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as follows. Care must be taken in writing a callback function, callback
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functions run in interrupt context:
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.. code-block:: c
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void callback(int level, int statid, void *priv);
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Interrupt Generation
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~~~~~~~~~~~~~~~~~~~~
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The function :c:func:`vme_irq_generate` can be used to generate a VME interrupt
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at a given VME level and VME status ID.
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Location monitors
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-----------------
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The VME API provides the following functionality to configure the location
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monitor.
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Location Monitor Management
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The function :c:func:`vme_lm_request` is provided to request the use of a block
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of location monitors and :c:func:`vme_lm_free` to free them after they are no
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longer required. Each block may provide a number of location monitors,
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monitoring adjacent locations. The function :c:func:`vme_lm_count` can be used
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to determine how many locations are provided.
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Location Monitor Configuration
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Once a bank of location monitors has been allocated, the function
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:c:func:`vme_lm_set` is provided to configure the location and mode of the
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location monitor. The function :c:func:`vme_lm_get` can be used to retrieve
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existing settings.
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Location Monitor Use
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~~~~~~~~~~~~~~~~~~~~
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The function :c:func:`vme_lm_attach` enables a callback to be attached and
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:c:func:`vme_lm_detach` allows on to be detached from each location monitor
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location. Each location monitor can monitor a number of adjacent locations. The
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callback function is declared as follows.
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.. code-block:: c
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void callback(void *data);
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Slot Detection
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--------------
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The function :c:func:`vme_slot_num` returns the slot ID of the provided bridge.
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Bus Detection
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-------------
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The function :c:func:`vme_bus_num` returns the bus ID of the provided bridge.
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VME API
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-------
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.. kernel-doc:: drivers/staging/vme_user/vme.h
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:internal:
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.. kernel-doc:: drivers/staging/vme_user/vme.c
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:export:
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