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Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+=======================
+Z8530 Programming Guide
+=======================
+
+:Author: Alan Cox
+
+Introduction
+============
+
+The Z85x30 family synchronous/asynchronous controller chips are used on
+a large number of cheap network interface cards. The kernel provides a
+core interface layer that is designed to make it easy to provide WAN
+services using this chip.
+
+The current driver only support synchronous operation. Merging the
+asynchronous driver support into this code to allow any Z85x30 device to
+be used as both a tty interface and as a synchronous controller is a
+project for Linux post the 2.4 release
+
+Driver Modes
+============
+
+The Z85230 driver layer can drive Z8530, Z85C30 and Z85230 devices in
+three different modes. Each mode can be applied to an individual channel
+on the chip (each chip has two channels).
+
+The PIO synchronous mode supports the most common Z8530 wiring. Here the
+chip is interface to the I/O and interrupt facilities of the host
+machine but not to the DMA subsystem. When running PIO the Z8530 has
+extremely tight timing requirements. Doing high speeds, even with a
+Z85230 will be tricky. Typically you should expect to achieve at best
+9600 baud with a Z8C530 and 64Kbits with a Z85230.
+
+The DMA mode supports the chip when it is configured to use dual DMA
+channels on an ISA bus. The better cards tend to support this mode of
+operation for a single channel. With DMA running the Z85230 tops out
+when it starts to hit ISA DMA constraints at about 512Kbits. It is worth
+noting here that many PC machines hang or crash when the chip is driven
+fast enough to hold the ISA bus solid.
+
+Transmit DMA mode uses a single DMA channel. The DMA channel is used for
+transmission as the transmit FIFO is smaller than the receive FIFO. it
+gives better performance than pure PIO mode but is nowhere near as ideal
+as pure DMA mode.
+
+Using the Z85230 driver
+=======================
+
+The Z85230 driver provides the back end interface to your board. To
+configure a Z8530 interface you need to detect the board and to identify
+its ports and interrupt resources. It is also your problem to verify the
+resources are available.
+
+Having identified the chip you need to fill in a struct z8530_dev,
+which describes each chip. This object must exist until you finally
+shutdown the board. Firstly zero the active field. This ensures nothing
+goes off without you intending it. The irq field should be set to the
+interrupt number of the chip. (Each chip has a single interrupt source
+rather than each channel). You are responsible for allocating the
+interrupt line. The interrupt handler should be set to
+:c:func:`z8530_interrupt()`. The device id should be set to the
+z8530_dev structure pointer. Whether the interrupt can be shared or not
+is board dependent, and up to you to initialise.
+
+The structure holds two channel structures. Initialise chanA.ctrlio and
+chanA.dataio with the address of the control and data ports. You can or
+this with Z8530_PORT_SLEEP to indicate your interface needs the 5uS
+delay for chip settling done in software. The PORT_SLEEP option is
+architecture specific. Other flags may become available on future
+platforms, eg for MMIO. Initialise the chanA.irqs to &z8530_nop to
+start the chip up as disabled and discarding interrupt events. This
+ensures that stray interrupts will be mopped up and not hang the bus.
+Set chanA.dev to point to the device structure itself. The private and
+name field you may use as you wish. The private field is unused by the
+Z85230 layer. The name is used for error reporting and it may thus make
+sense to make it match the network name.
+
+Repeat the same operation with the B channel if your chip has both
+channels wired to something useful. This isn't always the case. If it is
+not wired then the I/O values do not matter, but you must initialise
+chanB.dev.
+
+If your board has DMA facilities then initialise the txdma and rxdma
+fields for the relevant channels. You must also allocate the ISA DMA
+channels and do any necessary board level initialisation to configure
+them. The low level driver will do the Z8530 and DMA controller
+programming but not board specific magic.
+
+Having initialised the device you can then call
+:c:func:`z8530_init()`. This will probe the chip and reset it into
+a known state. An identification sequence is then run to identify the
+chip type. If the checks fail to pass the function returns a non zero
+error code. Typically this indicates that the port given is not valid.
+After this call the type field of the z8530_dev structure is
+initialised to either Z8530, Z85C30 or Z85230 according to the chip
+found.
+
+Once you have called z8530_init you can also make use of the utility
+function :c:func:`z8530_describe()`. This provides a consistent
+reporting format for the Z8530 devices, and allows all the drivers to
+provide consistent reporting.
+
+Attaching Network Interfaces
+============================
+
+If you wish to use the network interface facilities of the driver, then
+you need to attach a network device to each channel that is present and
+in use. In addition to use the generic HDLC you need to follow some
+additional plumbing rules. They may seem complex but a look at the
+example hostess_sv11 driver should reassure you.
+
+The network device used for each channel should be pointed to by the
+netdevice field of each channel. The hdlc-> priv field of the network
+device points to your private data - you will need to be able to find
+your private data from this.
+
+The way most drivers approach this particular problem is to create a
+structure holding the Z8530 device definition and put that into the
+private field of the network device. The network device fields of the
+channels then point back to the network devices.
+
+If you wish to use the generic HDLC then you need to register the HDLC
+device.
+
+Before you register your network device you will also need to provide
+suitable handlers for most of the network device callbacks. See the
+network device documentation for more details on this.
+
+Configuring And Activating The Port
+===================================
+
+The Z85230 driver provides helper functions and tables to load the port
+registers on the Z8530 chips. When programming the register settings for
+a channel be aware that the documentation recommends initialisation
+orders. Strange things happen when these are not followed.
+
+:c:func:`z8530_channel_load()` takes an array of pairs of
+initialisation values in an array of u8 type. The first value is the
+Z8530 register number. Add 16 to indicate the alternate register bank on
+the later chips. The array is terminated by a 255.
+
+The driver provides a pair of public tables. The z8530_hdlc_kilostream
+table is for the UK 'Kilostream' service and also happens to cover most
+other end host configurations. The z8530_hdlc_kilostream_85230 table
+is the same configuration using the enhancements of the 85230 chip. The
+configuration loaded is standard NRZ encoded synchronous data with HDLC
+bitstuffing. All of the timing is taken from the other end of the link.
+
+When writing your own tables be aware that the driver internally tracks
+register values. It may need to reload values. You should therefore be
+sure to set registers 1-7, 9-11, 14 and 15 in all configurations. Where
+the register settings depend on DMA selection the driver will update the
+bits itself when you open or close. Loading a new table with the
+interface open is not recommended.
+
+There are three standard configurations supported by the core code. In
+PIO mode the interface is programmed up to use interrupt driven PIO.
+This places high demands on the host processor to avoid latency. The
+driver is written to take account of latency issues but it cannot avoid
+latencies caused by other drivers, notably IDE in PIO mode. Because the
+drivers allocate buffers you must also prevent MTU changes while the
+port is open.
+
+Once the port is open it will call the rx_function of each channel
+whenever a completed packet arrived. This is invoked from interrupt
+context and passes you the channel and a network buffer (struct
+sk_buff) holding the data. The data includes the CRC bytes so most
+users will want to trim the last two bytes before processing the data.
+This function is very timing critical. When you wish to simply discard
+data the support code provides the function
+:c:func:`z8530_null_rx()` to discard the data.
+
+To active PIO mode sending and receiving the ``z8530_sync_open`` is called.
+This expects to be passed the network device and the channel. Typically
+this is called from your network device open callback. On a failure a
+non zero error status is returned.
+The :c:func:`z8530_sync_close()` function shuts down a PIO
+channel. This must be done before the channel is opened again and before
+the driver shuts down and unloads.
+
+The ideal mode of operation is dual channel DMA mode. Here the kernel
+driver will configure the board for DMA in both directions. The driver
+also handles ISA DMA issues such as controller programming and the
+memory range limit for you. This mode is activated by calling the
+:c:func:`z8530_sync_dma_open()` function. On failure a non zero
+error value is returned. Once this mode is activated it can be shut down
+by calling the :c:func:`z8530_sync_dma_close()`. You must call
+the close function matching the open mode you used.
+
+The final supported mode uses a single DMA channel to drive the transmit
+side. As the Z85C30 has a larger FIFO on the receive channel this tends
+to increase the maximum speed a little. This is activated by calling the
+``z8530_sync_txdma_open``. This returns a non zero error code on failure. The
+:c:func:`z8530_sync_txdma_close()` function closes down the Z8530
+interface from this mode.
+
+Network Layer Functions
+=======================
+
+The Z8530 layer provides functions to queue packets for transmission.
+The driver internally buffers the frame currently being transmitted and
+one further frame (in order to keep back to back transmission running).
+Any further buffering is up to the caller.
+
+The function :c:func:`z8530_queue_xmit()` takes a network buffer
+in sk_buff format and queues it for transmission. The caller must
+provide the entire packet with the exception of the bitstuffing and CRC.
+This is normally done by the caller via the generic HDLC interface
+layer. It returns 0 if the buffer has been queued and non zero values
+for queue full. If the function accepts the buffer it becomes property
+of the Z8530 layer and the caller should not free it.
+
+The function :c:func:`z8530_get_stats()` returns a pointer to an
+internally maintained per interface statistics block. This provides most
+of the interface code needed to implement the network layer get_stats
+callback.
+
+Porting The Z8530 Driver
+========================
+
+The Z8530 driver is written to be portable. In DMA mode it makes
+assumptions about the use of ISA DMA. These are probably warranted in
+most cases as the Z85230 in particular was designed to glue to PC type
+machines. The PIO mode makes no real assumptions.
+
+Should you need to retarget the Z8530 driver to another architecture the
+only code that should need changing are the port I/O functions. At the
+moment these assume PC I/O port accesses. This may not be appropriate
+for all platforms. Replacing :c:func:`z8530_read_port()` and
+``z8530_write_port`` is intended to be all that is required to port
+this driver layer.
+
+Known Bugs And Assumptions
+==========================
+
+Interrupt Locking
+    The locking in the driver is done via the global cli/sti lock. This
+    makes for relatively poor SMP performance. Switching this to use a
+    per device spin lock would probably materially improve performance.
+
+Occasional Failures
+    We have reports of occasional failures when run for very long
+    periods of time and the driver starts to receive junk frames. At the
+    moment the cause of this is not clear.
+
+Public Functions Provided
+=========================
+
+.. kernel-doc:: drivers/net/wan/z85230.c
+   :export:
+
+Internal Functions
+==================
+
+.. kernel-doc:: drivers/net/wan/z85230.c
+   :internal: