DM9000: Add documentation for the driver.

Add Documentation/networking/dm9000.txt for the DM9000
network driver.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

diff --git a/Documentation/networking/dm9000.txt b/Documentation/networking/dm9000.txt
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+DM9000 Network driver
+=====================
+
+Copyright 2008 Simtec Electronics,
+         Ben Dooks <ben@simtec.co.uk> <ben-linux@fluff.org>
+
+
+Introduction
+------------
+
+This file describes how to use the DM9000 platform-device based network driver
+that is contained in the files drivers/net/dm9000.c and drivers/net/dm9000.h.
+
+The driver supports three DM9000 variants, the DM9000E which is the first chip
+supported as well as the newer DM9000A and DM9000B devices. It is currently
+maintained and tested by Ben Dooks, who should be CC: to any patches for this
+driver.
+
+
+Defining the platform device
+----------------------------
+
+The minimum set of resources attached to the platform device are as follows:
+
+    1) The physical address of the address register
+    2) The physical address of the data register
+    3) The IRQ line the device's interrupt pin is connected to.
+
+These resources should be specified in that order, as the ordering of the
+two address regions is important (the driver expects these to be address
+and then data).
+
+An example from arch/arm/mach-s3c2410/mach-bast.c is:
+
+static struct resource bast_dm9k_resource[] = {
+       [0] = {
+               .start = S3C2410_CS5 + BAST_PA_DM9000,
+               .end   = S3C2410_CS5 + BAST_PA_DM9000 + 3,
+               .flags = IORESOURCE_MEM,
+       },
+       [1] = {
+               .start = S3C2410_CS5 + BAST_PA_DM9000 + 0x40,
+               .end   = S3C2410_CS5 + BAST_PA_DM9000 + 0x40 + 0x3f,
+               .flags = IORESOURCE_MEM,
+       },
+       [2] = {
+               .start = IRQ_DM9000,
+               .end   = IRQ_DM9000,
+               .flags = IORESOURCE_IRQ | IORESOURCE_IRQ_HIGHLEVEL,
+       }
+};
+
+static struct platform_device bast_device_dm9k = {
+       .name           = "dm9000",
+       .id             = 0,
+       .num_resources  = ARRAY_SIZE(bast_dm9k_resource),
+       .resource       = bast_dm9k_resource,
+};
+
+Note the setting of the IRQ trigger flag in bast_dm9k_resource[2].flags,
+as this will generate a warning if it is not present. The trigger from
+the flags field will be passed to request_irq() when registering the IRQ
+handler to ensure that the IRQ is setup correctly.
+
+This shows a typical platform device, without the optional configuration
+platform data supplied. The next example uses the same resources, but adds
+the optional platform data to pass extra configuration data:
+
+static struct dm9000_plat_data bast_dm9k_platdata = {
+       .flags          = DM9000_PLATF_16BITONLY,
+};
+
+static struct platform_device bast_device_dm9k = {
+       .name           = "dm9000",
+       .id             = 0,
+       .num_resources  = ARRAY_SIZE(bast_dm9k_resource),
+       .resource       = bast_dm9k_resource,
+       .dev            = {
+               .platform_data = &bast_dm9k_platdata,
+       }
+};
+
+The platform data is defined in include/linux/dm9000.h and described below.
+
+
+Platform data
+-------------
+
+Extra platform data for the DM9000 can describe the IO bus width to the
+device, whether or not an external PHY is attached to the device and
+the availability of an external configuration EEPROM.
+
+The flags for the platform data .flags field are as follows:
+
+DM9000_PLATF_8BITONLY
+
+       The IO should be done with 8bit operations.
+
+DM9000_PLATF_16BITONLY
+
+       The IO should be done with 16bit operations.
+
+DM9000_PLATF_32BITONLY
+
+       The IO should be done with 32bit operations.
+
+DM9000_PLATF_EXT_PHY
+
+       The chip is connected to an external PHY.
+
+DM9000_PLATF_NO_EEPROM
+
+       This can be used to signify that the board does not have an
+       EEPROM, or that the EEPROM should be hidden from the user.
+
+DM9000_PLATF_SIMPLE_PHY
+
+       Switch to using the simpler PHY polling method which does not
+       try and read the MII PHY state regularly. This is only available
+       when using the internal PHY. See the section on link state polling
+       for more information.
+
+       The config symbol DM9000_FORCE_SIMPLE_PHY_POLL, Kconfig entry
+       "Force simple NSR based PHY polling" allows this flag to be
+       forced on at build time.
+
+
+PHY Link state polling
+----------------------
+
+The driver keeps track of the link state and informs the network core
+about link (carrier) availablilty. This is managed by several methods
+depending on the version of the chip and on which PHY is being used.
+
+For the internal PHY, the original (and currently default) method is
+to read the MII state, either when the status changes if we have the
+necessary interrupt support in the chip or every two seconds via a
+periodic timer.
+
+To reduce the overhead for the internal PHY, there is now the option
+of using the DM9000_FORCE_SIMPLE_PHY_POLL config, or DM9000_PLATF_SIMPLE_PHY
+platform data option to read the summary information without the
+expensive MII accesses. This method is faster, but does not print
+as much information.
+
+When using an external PHY, the driver currently has to poll the MII
+link status as there is no method for getting an interrupt on link change.
+
+
+DM9000A / DM9000B
+-----------------
+
+These chips are functionally similar to the DM9000E and are supported easily
+by the same driver. The features are:
+
+   1) Interrupt on internal PHY state change. This means that the periodic
+      polling of the PHY status may be disabled on these devices when using
+      the internal PHY.
+
+   2) TCP/UDP checksum offloading, which the driver does not currently support.
+
+
+ethtool
+-------
+
+The driver supports the ethtool interface for access to the driver
+state information, the PHY state and the EEPROM.