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+Parport
++++++++
+
+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.
+
+
+modprobe
+--------
+
+If you use modprobe , you will find it useful to add lines as below to a
+configuration file in /etc/modprobe.d/ directory::
+
+ alias parport_lowlevel parport_pc
+ options parport_pc io=0x378,0x278 irq=7,auto
+
+modprobe will 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
+
+.. tabularcolumns:: |p{4.0cm}|p{13.5cm}|
+
+======================= =======================================================
+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:
+
+- polling
+- interrupt-driven, protocol in software
+- interrupt-driven, protocol in hardware using PIO
+- 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_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