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+The `parport' code provides parallel-port support under Linux.  This
+includes the ability to share one port between multiple device
+drivers.
+
+You can pass parameters to the parport code to override its automatic
+detection of your hardware.  This is particularly useful if you want
+to use IRQs, since in general these can't be autoprobed successfully.
+By default IRQs are not used even if they _can_ be probed.  This is
+because there are a lot of people using the same IRQ for their
+parallel port and a sound card or network card.
+
+The parport code is split into two parts: generic (which deals with
+port-sharing) and architecture-dependent (which deals with actually
+using the port).
+
+
+Parport as modules
+==================
+
+If you load the parport code as a module, say
+
+        # insmod parport
+
+to load the generic parport code.  You then must load the
+architecture-dependent code with (for example):
+
+        # insmod parport_pc io=0x3bc,0x378,0x278 irq=none,7,auto
+
+to tell the parport code that you want three PC-style ports, one at
+0x3bc with no IRQ, one at 0x378 using IRQ 7, and one at 0x278 with an
+auto-detected IRQ.  Currently, PC-style (parport_pc), Sun `bpp',
+Amiga, Atari, and MFC3 hardware is supported.
+
+PCI parallel I/O card support comes from parport_pc.  Base I/O
+addresses should not be specified for supported PCI cards since they
+are automatically detected.
+
+
+KMod
+----
+
+If you use kmod, you will find it useful to edit /etc/modprobe.conf.
+Here is an example of the lines that need to be added:
+
+        alias parport_lowlevel parport_pc
+        options parport_pc io=0x378,0x278 irq=7,auto
+
+KMod will then automatically load parport_pc (with the options
+"io=0x378,0x278 irq=7,auto") whenever a parallel port device driver
+(such as lp) is loaded.
+
+Note that these are example lines only!  You shouldn't in general need
+to specify any options to parport_pc in order to be able to use a
+parallel port.
+
+
+Parport probe [optional]
+-------------
+
+In 2.2 kernels there was a module called parport_probe, which was used
+for collecting IEEE 1284 device ID information.  This has now been
+enhanced and now lives with the IEEE 1284 support.  When a parallel
+port is detected, the devices that are connected to it are analysed,
+and information is logged like this:
+
+        parport0: Printer, BJC-210 (Canon)
+
+The probe information is available from files in /proc/sys/dev/parport/.
+
+
+Parport linked into the kernel statically
+=========================================
+
+If you compile the parport code into the kernel, then you can use
+kernel boot parameters to get the same effect.  Add something like the
+following to your LILO command line:
+
+        parport=0x3bc parport=0x378,7 parport=0x278,auto,nofifo
+
+You can have many `parport=...' statements, one for each port you want
+to add.  Adding `parport=0' to the kernel command-line will disable
+parport support entirely.  Adding `parport=auto' to the kernel
+command-line will make parport use any IRQ lines or DMA channels that
+it auto-detects.
+
+
+Files in /proc
+==============
+
+If you have configured the /proc filesystem into your kernel, you will
+see a new directory entry: /proc/sys/dev/parport.  In there will be a
+directory entry for each parallel port for which parport is
+configured.  In each of those directories are a collection of files
+describing that parallel port.
+
+The /proc/sys/dev/parport directory tree looks like:
+
+parport
+|-- default
+|   |-- spintime
+|   `-- timeslice
+|-- parport0
+|   |-- autoprobe
+|   |-- autoprobe0
+|   |-- autoprobe1
+|   |-- autoprobe2
+|   |-- autoprobe3
+|   |-- devices
+|   |   |-- active
+|   |   `-- lp
+|   |       `-- timeslice
+|   |-- base-addr
+|   |-- irq
+|   |-- dma
+|   |-- modes
+|   `-- spintime
+`-- parport1
+    |-- autoprobe
+    |-- autoprobe0
+    |-- autoprobe1
+    |-- autoprobe2
+    |-- autoprobe3
+    |-- devices
+    |   |-- active
+    |   `-- ppa
+    |       `-- timeslice
+    |-- base-addr
+    |-- irq
+    |-- dma
+    |-- modes
+    `-- spintime
+
+
+File:           Contents:
+
+devices/active  A list of the device drivers using that port.  A "+"
+                will appear by the name of the device currently using
+                the port (it might not appear against any).  The
+                string "none" means that there are no device drivers
+                using that port.
+
+base-addr       Parallel port's base address, or addresses if the port
+                has more than one in which case they are separated
+                with tabs.  These values might not have any sensible
+                meaning for some ports.
+
+irq             Parallel port's IRQ, or -1 if none is being used.
+
+dma             Parallel port's DMA channel, or -1 if none is being
+                used.
+
+modes           Parallel port's hardware modes, comma-separated,
+                meaning:
+
+                PCSPP           PC-style SPP registers are available.
+                TRISTATE        Port is bidirectional.
+                COMPAT          Hardware acceleration for printers is
+                                available and will be used.
+                EPP             Hardware acceleration for EPP protocol
+                                is available and will be used.
+                ECP             Hardware acceleration for ECP protocol
+                                is available and will be used.
+                DMA             DMA is available and will be used.
+
+                Note that the current implementation will only take
+                advantage of COMPAT and ECP modes if it has an IRQ
+                line to use.
+
+autoprobe       Any IEEE-1284 device ID information that has been
+                acquired from the (non-IEEE 1284.3) device.
+
+autoprobe[0-3]  IEEE 1284 device ID information retrieved from
+                daisy-chain devices that conform to IEEE 1284.3.
+
+spintime        The number of microseconds to busy-loop while waiting
+                for the peripheral to respond.  You might find that
+                adjusting this improves performance, depending on your
+                peripherals.  This is a port-wide setting, i.e. it
+                applies to all devices on a particular port.
+
+timeslice       The number of milliseconds that a device driver is
+                allowed to keep a port claimed for.  This is advisory,
+                and driver can ignore it if it must.
+
+default/*       The defaults for spintime and timeslice. When a new
+                port is registered, it picks up the default spintime.
+                When a new device is registered, it picks up the
+                default timeslice.
+
+Device drivers
+==============
+
+Once the parport code is initialised, you can attach device drivers to
+specific ports.  Normally this happens automatically; if the lp driver
+is loaded it will create one lp device for each port found.  You can
+override this, though, by using parameters either when you load the lp
+driver:
+
+        # insmod lp parport=0,2
+
+or on the LILO command line:
+
+        lp=parport0 lp=parport2
+
+Both the above examples would inform lp that you want /dev/lp0 to be
+the first parallel port, and /dev/lp1 to be the _third_ parallel port,
+with no lp device associated with the second port (parport1).  Note
+that this is different to the way older kernels worked; there used to
+be a static association between the I/O port address and the device
+name, so /dev/lp0 was always the port at 0x3bc.  This is no longer the
+case - if you only have one port, it will default to being /dev/lp0,
+regardless of base address.
+
+Also:
+
+ * If you selected the IEEE 1284 support at compile time, you can say
+   `lp=auto' on the kernel command line, and lp will create devices
+   only for those ports that seem to have printers attached.
+
+ * If you give PLIP the `timid' parameter, either with `plip=timid' on
+   the command line, or with `insmod plip timid=1' when using modules,
+   it will avoid any ports that seem to be in use by other devices.
+
+ * IRQ autoprobing works only for a few port types at the moment.
+
+Reporting printer problems with parport
+=======================================
+
+If you are having problems printing, please go through these steps to
+try to narrow down where the problem area is.
+
+When reporting problems with parport, really you need to give all of
+the messages that parport_pc spits out when it initialises.  There are
+several code paths:
+
+o polling
+o interrupt-driven, protocol in software
+o interrupt-driven, protocol in hardware using PIO
+o interrupt-driven, protocol in hardware using DMA
+
+The kernel messages that parport_pc logs give an indication of which
+code path is being used. (They could be a lot better actually..)
+
+For normal printer protocol, having IEEE 1284 modes enabled or not
+should not make a difference.
+
+To turn off the 'protocol in hardware' code paths, disable
+CONFIG_PARPORT_PC_FIFO.  Note that when they are enabled they are not
+necessarily _used_; it depends on whether the hardware is available,
+enabled by the BIOS, and detected by the driver.
+
+So, to start with, disable CONFIG_PARPORT_PC_FIFO, and load parport_pc
+with 'irq=none'. See if printing works then.  It really should,
+because this is the simplest code path.
+
+If that works fine, try with 'io=0x378 irq=7' (adjust for your
+hardware), to make it use interrupt-driven in-software protocol.
+
+If _that_ works fine, then one of the hardware modes isn't working
+right.  Enable CONFIG_PARPORT_PC_FIFO (no, it isn't a module option,
+and yes, it should be), set the port to ECP mode in the BIOS and note
+the DMA channel, and try with:
+
+    io=0x378 irq=7 dma=none (for PIO)
+    io=0x378 irq=7 dma=3 (for DMA)
+--
+philb@gnu.org
+tim@cyberelk.net