path: root/Documentation/parport.txt
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/parport.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+The `parport' code provides parallel-port support under Linux. This
+includes the ability to share one port between multiple device
+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.
+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:
+|-- 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
+ # 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.
+ * 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)