xref: /openbmc/linux/Documentation/driver-api/vme.rst (revision 35ba63b8)

VME Device Drivers
==================

Driver registration
-------------------

As with other subsystems within the Linux kernel, VME device drivers register
with the VME subsystem, typically called from the devices init routine.  This is
achieved via a call to :c:func:`vme_register_driver`.

A pointer to a structure of type :c:type:`struct vme_driver <vme_driver>` must
be provided to the registration function. Along with the maximum number of
devices your driver is able to support.

At the minimum, the '.name', '.match' and '.probe' elements of
:c:type:`struct vme_driver <vme_driver>` should be correctly set. The '.name'
element is a pointer to a string holding the device driver's name.

The '.match' function allows control over which VME devices should be registered
with the driver. The match function should return 1 if a device should be
probed and 0 otherwise. This example match function (from vme_user.c) limits
the number of devices probed to one:

.. code-block:: c

	#define USER_BUS_MAX	1
	...
	static int vme_user_match(struct vme_dev *vdev)
	{
		if (vdev->id.num >= USER_BUS_MAX)
			return 0;
		return 1;
	}

The '.probe' element should contain a pointer to the probe routine. The
probe routine is passed a :c:type:`struct vme_dev <vme_dev>` pointer as an
argument.

Here, the 'num' field refers to the sequential device ID for this specific
driver. The bridge number (or bus number) can be accessed using
dev->bridge->num.

A function is also provided to unregister the driver from the VME core called
:c:func:`vme_unregister_driver` and should usually be called from the device
driver's exit routine.


Resource management
-------------------

Once a driver has registered with the VME core the provided match routine will
be called the number of times specified during the registration. If a match
succeeds, a non-zero value should be returned. A zero return value indicates
failure. For all successful matches, the probe routine of the corresponding
driver is called. The probe routine is passed a pointer to the devices
device structure. This pointer should be saved, it will be required for
requesting VME resources.

The driver can request ownership of one or more master windows
(:c:func:`vme_master_request`), slave windows (:c:func:`vme_slave_request`)
and/or dma channels (:c:func:`vme_dma_request`). Rather than allowing the device
driver to request a specific window or DMA channel (which may be used by a
different driver) the API allows a resource to be assigned based on the required
attributes of the driver in question. For slave windows these attributes are
split into the VME address spaces that need to be accessed in 'aspace' and VME
bus cycle types required in 'cycle'. Master windows add a further set of
attributes in 'width' specifying the required data transfer widths. These
attributes are defined as bitmasks and as such any combination of the
attributes can be requested for a single window, the core will assign a window
that meets the requirements, returning a pointer of type vme_resource that
should be used to identify the allocated resource when it is used. For DMA
controllers, the request function requires the potential direction of any
transfers to be provided in the route attributes. This is typically VME-to-MEM
and/or MEM-to-VME, though some hardware can support VME-to-VME and MEM-to-MEM
transfers as well as test pattern generation. If an unallocated window fitting
the requirements can not be found a NULL pointer will be returned.

Functions are also provided to free window allocations once they are no longer
required. These functions (:c:func:`vme_master_free`, :c:func:`vme_slave_free`
and :c:func:`vme_dma_free`) should be passed the pointer to the resource
provided during resource allocation.


Master windows
--------------

Master windows provide access from the local processor[s] out onto the VME bus.
The number of windows available and the available access modes is dependent on
the underlying chipset. A window must be configured before it can be used.


Master window configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once a master window has been assigned :c:func:`vme_master_set` can be used to
configure it and :c:func:`vme_master_get` to retrieve the current settings. The
address spaces, transfer widths and cycle types are the same as described
under resource management, however some of the options are mutually exclusive.
For example, only one address space may be specified.


Master window access
~~~~~~~~~~~~~~~~~~~~

The function :c:func:`vme_master_read` can be used to read from and
:c:func:`vme_master_write` used to write to configured master windows.

In addition to simple reads and writes, :c:func:`vme_master_rmw` is provided to
do a read-modify-write transaction. Parts of a VME window can also be mapped
into user space memory using :c:func:`vme_master_mmap`.


Slave windows
-------------

Slave windows provide devices on the VME bus access into mapped portions of the
local memory. The number of windows available and the access modes that can be
used is dependent on the underlying chipset. A window must be configured before
it can be used.


Slave window configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~

Once a slave window has been assigned :c:func:`vme_slave_set` can be used to
configure it and :c:func:`vme_slave_get` to retrieve the current settings.

The address spaces, transfer widths and cycle types are the same as described
under resource management, however some of the options are mutually exclusive.
For example, only one address space may be specified.


Slave window buffer allocation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Functions are provided to allow the user to allocate
(:c:func:`vme_alloc_consistent`) and free (:c:func:`vme_free_consistent`)
contiguous buffers which will be accessible by the VME bridge. These functions
do not have to be used, other methods can be used to allocate a buffer, though
care must be taken to ensure that they are contiguous and accessible by the VME
bridge.


Slave window access
~~~~~~~~~~~~~~~~~~~

Slave windows map local memory onto the VME bus, the standard methods for
accessing memory should be used.


DMA channels
------------

The VME DMA transfer provides the ability to run link-list DMA transfers. The
API introduces the concept of DMA lists. Each DMA list is a link-list which can
be passed to a DMA controller. Multiple lists can be created, extended,
executed, reused and destroyed.


List Management
~~~~~~~~~~~~~~~

The function :c:func:`vme_new_dma_list` is provided to create and
:c:func:`vme_dma_list_free` to destroy DMA lists. Execution of a list will not
automatically destroy the list, thus enabling a list to be reused for repetitive
tasks.


List Population
~~~~~~~~~~~~~~~

An item can be added to a list using :c:func:`vme_dma_list_add` (the source and
destination attributes need to be created before calling this function, this is
covered under "Transfer Attributes").

.. note::

	The detailed attributes of the transfers source and destination
	are not checked until an entry is added to a DMA list, the request
	for a DMA channel purely checks the directions in which the
	controller is expected to transfer data. As a result it is
	possible for this call to return an error, for example if the
	source or destination is in an unsupported VME address space.

Transfer Attributes
~~~~~~~~~~~~~~~~~~~

The attributes for the source and destination are handled separately from adding
an item to a list. This is due to the diverse attributes required for each type
of source and destination. There are functions to create attributes for PCI, VME
and pattern sources and destinations (where appropriate):

 - PCI source or destination: :c:func:`vme_dma_pci_attribute`
 - VME source or destination: :c:func:`vme_dma_vme_attribute`
 - Pattern source: :c:func:`vme_dma_pattern_attribute`

The function :c:func:`vme_dma_free_attribute` should be used to free an
attribute.


List Execution
~~~~~~~~~~~~~~

The function :c:func:`vme_dma_list_exec` queues a list for execution and will
return once the list has been executed.


Interrupts
----------

The VME API provides functions to attach and detach callbacks to specific VME
level and status ID combinations and for the generation of VME interrupts with
specific VME level and status IDs.


Attaching Interrupt Handlers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The function :c:func:`vme_irq_request` can be used to attach and
:c:func:`vme_irq_free` to free a specific VME level and status ID combination.
Any given combination can only be assigned a single callback function. A void
pointer parameter is provided, the value of which is passed to the callback
function, the use of this pointer is user undefined. The callback parameters are
as follows. Care must be taken in writing a callback function, callback
functions run in interrupt context:

.. code-block:: c

	void callback(int level, int statid, void *priv);


Interrupt Generation
~~~~~~~~~~~~~~~~~~~~

The function :c:func:`vme_irq_generate` can be used to generate a VME interrupt
at a given VME level and VME status ID.


Location monitors
-----------------

The VME API provides the following functionality to configure the location
monitor.


Location Monitor Management
~~~~~~~~~~~~~~~~~~~~~~~~~~~

The function :c:func:`vme_lm_request` is provided to request the use of a block
of location monitors and :c:func:`vme_lm_free` to free them after they are no
longer required. Each block may provide a number of location monitors,
monitoring adjacent locations. The function :c:func:`vme_lm_count` can be used
to determine how many locations are provided.


Location Monitor Configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once a bank of location monitors has been allocated, the function
:c:func:`vme_lm_set` is provided to configure the location and mode of the
location monitor. The function :c:func:`vme_lm_get` can be used to retrieve
existing settings.


Location Monitor Use
~~~~~~~~~~~~~~~~~~~~

The function :c:func:`vme_lm_attach` enables a callback to be attached and
:c:func:`vme_lm_detach` allows on to be detached from each location monitor
location. Each location monitor can monitor a number of adjacent locations. The
callback function is declared as follows.

.. code-block:: c

	void callback(void *data);


Slot Detection
--------------

The function :c:func:`vme_slot_num` returns the slot ID of the provided bridge.


Bus Detection
-------------

The function :c:func:`vme_bus_num` returns the bus ID of the provided bridge.


VME API
-------

.. kernel-doc:: drivers/staging/vme_user/vme.h
   :internal:

.. kernel-doc:: drivers/staging/vme_user/vme.c
   :export: