android_kernel_xiaomi_sm8350/Documentation/admin-guide/parport.rst

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