Plug-and-Play-HOWTO: How Do I Find Devices and How Are They Configured?

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## 6. How Do I Find Devices and How Are They Configured?

## 6.1 Finding and How-Configured Are Related

Once you find your hardware, the same program that found it usually tells you how it's configured. So finding out how it's configured is usually the same procedure as finding the hardware.

## 6.2 Devices May Have Two "Configurations"

Here "configuration" means the assignment of PnP bus-resources (addresses, IRQs, and DMAs). For each device, there are two parts to the configuration question:

1. What does the driver think the hardware configuration is?
2. What configuration (if any) is actually set in the device hardware?

Each part should have the same answer (the same configuration). The configuration of the device hardware and its driver should obviously be the same (and usually is). But if things are not working right, it could be because there's a difference. This means that the driver has incorrect information about the actual configuration of the hardware. This spells trouble. If the software you use doesn't adequately tell you what's wrong (or automatically configure it correctly) then you need to investigate how your hardware devices and their drivers are configured. While Linux device drivers should "tell all", in some cases it may not be easy to determine what has been set in the hardware.

Another problem is that when you view configuration messages on the screen you need to know whether the reported configuration is that of the device driver, the device hardware, or both. If the device driver has either set the configuration in the hardware or has otherwise checked the hardware then the driver should have the correct information.

But sometimes the driver has been provided incorrect resources by a script, configuration file, by incorrect resource parameters given to a module, or perhaps just hasn't been told what the resources are and tries to use incorrect default resources. For example, one can uses "setserial" to tell the serial port driver an incorrect resource configuration and the driver accepts it without question. But the serial port doesn't work right (if at all).

## 6.3 Finding Hardware

A common problem is that the software doesn't detect your device and/or determine the right driver for it. For PnP devices, detecting them is easy via PnP software except for the unusual case where the hardware has been disabled. The BIOS can sometimes be set to disable PnP devices or a jumper/switch on the physical device itself could disable it. In such a cases, the hardware can't be detected at all until you either reconfigure the BIOS or change a jumper/switch.

Since the PCI bus is inherently PnP, there are no hidden devices. Even though PnP devices are easy to find by PnP methods, if the driver doesn't use PnP methods but uses the old method of probing for them at likely address, they may not be found. This is because that, until the resources are set in a PnP device (by the BIOS or Linux), the device may have no address at all, so probing at likely address yields nothing. For the old ISA bus, some of the devices may be non-PnP and thus the old probing methods may find them. So many drivers still probe at likely address, in addition to using PnP methods (= PnP probing which is sometimes also just called "probing").

Ways to Find Hardware Devices (and their configurations): (follow link to more details)

- Check the BIOS to make sure they are not disabled
- Watch the Boot-time Messages on the screen
- Look in The /proc Directory Tree
- Tools for Detecting and/or Configuring all Hardware lsdev, hwinfo, discover, kudzu
- Tools for Detecting and/or Configuring One Type of Hardware
- PCI: PCI Bus Inspection
- ISA Bus: ISA Bus Introduction
- ISA Bus: PnP cards
- ISA Bus: For Non-PnP Cards
- ISA Bus: For Cards with jumpers
- ISA Bus: If Neither PnP nor jumpers
- Use MS Windows

## 6.4 Boot-time Messages

Significant info on the configuration may be obtained by reading the messages from the BIOS and from Linux that appear on the screen when you first start the computer. These messages often flash by too fast to read but once they stop type Shift-PageUp a few times to scroll back to them. To scroll forward thru them type Shift-PageDown. Typing "dmesg" at any time to the shell prompt will show only the Linux kernel messages and may miss some of the most important ones (including ones from the BIOS). The messages from Linux may sometimes only show what the device driver thinks the configuration is, perhaps as told it via an incorrect configuration file. Checking log files in /var/log may also be useful.

For the PCI bus, the notation: 00:1a:0 means the PCI bus 00 (the main PCI bus), PCI card (or chip) 1a, and function 0 (the first device) on the card or chip. The 2nd device on the card (or chip) 08 would be: 00:08:1.

The BIOS messages display first and will show the actual hardware configuration at that time, but isapnp, or pci utilities, or device drivers may change it later. In some cases it doesn't show devices that the BIOS didn't configure.

If the BIOS messages don't show as you back up to the start of the BIOS messages using Shift-PageUp, try freezing them as they flash by, by hitting the "Pause" key as soon as the first words flash on the screen. Press any key to resume. It's often tricky to hit Pause exactly at the right time. Be sure to hold down the "Shift" key before hitting "Pause" since "Pause" is a shifted key. If you miss, hit Ctrl-Alt-Del when Linux starts booting to reboot and try again. Once the messages from Linux start to appear, it's too late to use "Pause" since it will not freeze the messages from Linux.

To set things in the BIOS such as IRQs reserved for legacy hardware, serial port addresses, etc. you need to get into the BIOS (CMOS) setup menus at boot time. Each BIOS brand has different keys you need to hold down to do this. There are lists on the Internet. Sometimes by freezing the BIOS messages or watching the screen, the key you need to press will be indicated in a message such as "Press DEL for setup". But it may flash by so fast that you miss it. Of course, you don't set stuff in the BIOS that you don't understand, or your PC may become disabled.

Messages from the BIOS at boot-time tell you how the hardware configuration was then. The current configuration may still be the same since Linux should hopefully accept what the BIOS has done if it's OK. Messages from Linux may be from drivers that used kernel PnP functions to inspect and/or set bus-resources. These should be correct, but beware of messages that only show what the driver was told from a configuration file. It could be wrong. Of course, if the device works fine, then it's likely configured the same as the driver.

## 6.5 The /proc Tree

Starting with Kernel 2.6, in addition to the /proc directory tree, there's also a /sys tree See The /sys Tree. These trees are useful for finding resource configurations and devices. The "files" in them represent data in the kernel memory and don't exist at all on you harddrive. Programs such as lspci get their info from the /proc tree so such programs should display the results in more readable form than directly inspecting the "files" in /proc. Here are 4 /proc "files" that show resources which have been registered in the kernel by device drivers.

Since Linux's plug-and-play works by letting device drivers allocate resources for their device, there may be no listing of resources used by some of your hardware if the driver hasn't yet requested that such resources be reserved. For the case of kernel modules (loadable device drivers), if the module hasn't loaded yet, the kernel doesn't know about any resources it needs. Sometimes, the module only loads when you start an application that needs it. So if certain hardware is missing from these "files" in /proc, it may mean that the hardware hasn't yet been used. For example, even though your floppy drive has a floppy disk in it and is ready to use, the interrupt for it will not show up unless its in use.

/pts shows I/O addresses. If there's a mistake (wrong address) it means trouble since the device will not get bytes sent to it.
/proc/iomem shows registered IO memory addresses.
/proc/interrupts shows the interrupts currently in use.
/proc/dma shows the dma (Direct Memory Access) ISA dma channel allocations.

In the past, the author observed the listing of interrupts that didn't exist. In some cases it showed that a few such interrupts were actually sent. This could be due to the issuing of erroneous interrupts due to hardware defects.

/proc/bus/ has subdirectories (subfolders) input/, pci/, and isapnp/. The format of most of the files in this directory is very cryptic, often just a copy of the bytes in the configuration space. So, use them only as a last resort. The input/ subdirectory has information on input devices such as the keyboard and mouse. It's not as cryptic as the other directories under /proc/bus/ and might yield some useful information about input devices that are PS2 or on the LPC bus (See LPC Bus). Unfortunately, what I've seen doesn't say that it's on the LPC bus when it likely is. In /pci/00/ there is one binary file for each pci device where the file names are the pci-slot-numbers (also called pci-slot-names). The 00 means pci bus 0.

## 6.6 The /sys Tree

Starting with kernel 2.6 there's a new /sys directory for PnP configuration. It's a sysfs type of file system and it's something like the /proc filesystem since the "files" represent information in the kernel memory and are not on your harddrive. But it's not as useful as the /proc filesystem. Originally (in the 2.5 kernels) it was called "driver file system" of type "driverfs".

In the sysfs, each device which exists on your system has it's own directory which contains files showing the resources allocated to it. Such device directories have names like 0000:00:12.0@ or 00:06@. What devices are these? The first is a PCI card in "slot" 12 of your PC. The slot may actually be labeled PCI2 inside your PC (2 instead of 12). That's because low numbered "slots" are used for built-in devices on the motherboard that don't use any physical slots. In this example, "slots" 1-10 would be built-in and actual slots 11-14 are labeled 1-4. By typing "lspci" you'll be able to match the numbers (like 0000:00:12.0) to names (like IDE interface). Type "lspci -v" or "lspci -vv" to see more.

Well then, what is 00:06 ? It's an ISA card (or built-in device) but it's not ISA slot 6 (like the PCI numbering). When a search was made for ISA-PNP devices, it was the 6th one found. More precisely, it was the 7th one found since there's a device numbered: 00:00. So how does one identify them? Well, you could type: "cat */*" and display all the files for all the devices, but even then you don't see the device names (but do see info from which you can identify them). This inconvenience will hopefully be fixed in the future.

Not only do these files supply information on the bus-resource configuration (in somewhat cryptic format) and drivers (in "driver" directories), but in the future, you should be able to use them to change the resource configuration. Right now (Aug 2004) you can't configure the PCI bus with it. A serious limitation is that per the present "driver model" you can't change the resource of a device that has been assigned to a driver which likely means that you'll need to unload the driver module in order to use it. If the driver is built in, there's no hope. These serious limitations will hopefully be eliminated in the future. In the kernel documentation is a file: "pnp.txt" telling how to configure. As of Aug. 2004, it was much out-of-date but the author is working on an update. Using the /sys tree to configure resources is known as the "Linux Plug and Play User Interface".

The other part of "Linux Plug and Play" is the kernel interface used by device drivers. This has changed a lot starting with kernel 2.6 but most drivers are still using the old interface (as of Aug. 2004). It's possible also for drivers (or you) to use the "user interface" which needs improvement.

## 6.7 PCI Bus Inspection

It's easy to find out what bus-resources have been assigned to devices on the PCI bus with the "lspci" and/or "scanpci" commands The options -v or -vv will show more detail. In some cases, "scanpci" will find a device that "lspci" can't find. That's because "scanpci" directly searches for devices on the pci bus (via the configuration space) and doesn't use data obtained by the kernel (where it could be wrong due to a kernel bug --I've just found such a case).

This info in more cryptic format is found in "files" located in the `/sys` and `/proc` trees. In `/sys/bus/pci/devices` the file `vendor` will contain the vendor id number such as 0x4B8C, etc. In still more cryptic format it's in `/proc/bus/pci`. Such information in older kernels prior to kernel 2.6, was in `/proc/pci` (non-cryptic but IRQs in hexadecimal) or in `/proc/buspci/devices` (cryptic display).

In most cases for PCI you will only see how the hardware is now configured and not what resources are required. In some cases you only see the base addresses (the starting addresses of the range) but not the ending addresses. If you see the entire range then you can determine how many bytes of address resources are needed.

## 6.8 ISA Bus Introduction

For cards on the ISA bus, it's not as simple as for the PCI bus which is inherently PnP. Later ISA cards were PnP but older ones were not. Also, some cards that are PnP had their PnP disabled by special software which runs only on MS. The non PnP cards are configured by jumpers on the card or by MS software.

## 6.9 ISA PnP cards

If it's a PnP card you may try running `pnpdump --dumpregs` but it's not a sure thing. The results may be seem cryptic but they can be deciphered. Don't confuse the read-port address which `pnpdump` uses for communication with PnP cards with the I/O address of the found device. They are not the same.

## 6.10 LPC Bus

LPC (Low Pin Count) is a bus-like interface often used on laptops and increasingly used on desktops too. To find out if you have LPC type "lspci" and look for "LPC". There are other words next to "LPC" such as "ISA Bridge ... LPC Interface Controller" or "LPC Bridge", etc. LPC is not really ISA but it substitutes for an ISA bus.

The old ISA bus was slow and devices that needed more speed were put on the newer PCI but. But devices that didn't need high speed were often implemented by chips on the motherboard and remained on the ISA bus even though there were no slots for any ISA cards. Then the LPC bus came along to replace what remained of the ISA bus. LPC is much smaller than ISA and just as fast since it runs at 4 times the clock speed of ISA. Its multiplexed bus for data/address and control is only 4 bits wide. To send a byte requires splitting the byte into 2 half-bytes and then putting them back together. So its clear why it's "Low Pin Count" = LPC. There's also a few other lines in the bus.

This small LPC interface is used for slow "legacy" devices such as serial ports, parallel ports, and floppy drives. So a computer using LPC will have all fast devices on the PCI bus, etc. and slow (legacy) devices on the LPC bus interface. All LPC devices will be on-board; there are no LPC slots.

LPC has no standards for Plug-and-Play configuring but says that the BIOS or ACPI should do the configuring. Devices on this bus sometimes use isapnp. Linux support for LPC as of late 2004 was very much incomplete but Linux has some support for the configuring aspects of ACPI. Sometimes a BIOS menu lets one manually PnP-configure devices on the LPC bus but it may not tell you that the device resides on LPC.

A major chip on the LPC bus is the superio chip which contains legacy IO devices: serial and parallel ports, floppy controller, keyboard controller, mice, etc. BIOS data may also reside on the LPC bus. The keyboard and mouse (input devices) should be listed in /proc/bus/input/devices but instead of seeing "lpc" it seems to show "isa0060/serio0, etc. even though it's on the lpc bus and not the isa bus.

## 6.11 X-bus

Before the LPC bus became popular, there was an "X-bus" (not covered in this HOWTO) which served the same purpose as the LPC bus but wasn't so compact as LPC. Some PCs have both LPC and an X-bus.

## 6.12 Non-PnP Cards

In contrast to PnP cards, non-PnP cards always have their resources set in the hardware. That is they always have an address and IRQ unless there is a jumper setting, etc. for disabling the device. Sometimes the resources used can be found by probing done by the device driver or by other software that does probing. For example "scanport" (Debian only ??) probes most IO port address and may find ISA devices. But be warned that it might hang your PC. Sometimes it will fail to find hardware that's actually there (since the hardware has the default 0xff in it's registers). Even if It finds the hardware it will not show the IRQ nor will it positively identify the hardware.

So one way to try to find such hardware is to start a driver, which may probe for such hardware. By looking at the boot-time messages, you might see a driver start and find the hardware. Otherwise, you may need to find a driver and start it (for example, by having it load as a module).

Finding the right driver may be difficult. Sometimes there just isn't any driver since some devices aren't (yet ?) supported by Linux. To determine which driver you need, look at any documentation which might identify the card. If this fails, look on the card itself, including important names/numbers on the chips. But the identification of the driver module you need may not be anywhere on the card. You could find the FCC id on the card and then search the Internet with the FCC id number to try to find more information about the card (or the chips on it).

## 6.13 Non-PnP Cards with jumpers

If the card has jumpers to set the resources (configuration) then one may look at how the jumpers are set. There are some cards that had both PnP and jumpers. They worked like jumper cards if PnP was somehow disabled. Sometimes a card has labels on it showing how to set the jumpers (or at least gives some clue). You may need the documentation that came with the card (either printed or on a floppy disk). Perhaps you can find it on the Internet.

## 6.14 Neither PnP nor jumpers

One the most difficult cases is where software running under MS has been used to configure either a non-PnP card or a PnP card where PnP has been disabled by the same MS software. So you can't configure it by PnP nor by jumpers. In this case your only hope is to probe for addresses as described in Non-PnP Cards. Or try to find the MS software that configured it.

## 6.15 Tools for Detecting and/or Configuring all Hardware

In a duplication of effort, various major distributions of Linux developed their own tools for detection and/or configuration of hardware. This configuring is usually a lot more than just the resource type configuring of Plug-and-Play. It's configuring in general which is mostly beyond the scope of this howto.

Then other distributions, such as Debian, might obtain copies of the tool and offer it to their users as an option, or as a troubleshooting tool. These tools likely make use of the standard Linux tools for detecting hardware such as "lspci". In the following list of tools, the name of the distribution that developed it is in parentheses, but the tool is likely available also in other distributions.

- hardinfo
- hwinfo (SuSE) detects move stuff than discover
- discover (Progeny, used by Debian)
- Kudzu (RedHat) detects and configures
- lsdev (standard Linux command)
- hwsetup-knoppix (Knoppix, based on Kudzu)

## 6.16 Tools for Detecting and Configuring One Type of Hardware

There are various tools available to find and possibly configure various type of devices. This configuring is configuring in general which is not covered by this howto.

- read-edid (get-edid): gets parameters of VESA monitors (except very old ones)
- sndconfig: for soundcards
- printtool: printers, must have X-window running
- pconf-detect: parallel ports
- gpm-mouse-test:detects and tests mice
- mdetect: detects and configures mice Does it know about the mice devices in /dev/input/?
- nictools-pci (and nictools-nopci) for ethernet cards
- hdparm: configure hard drive hardware
- hotplug: used by kernel
- xvidtune: tune video for use with Xwindows (See XFree86-Video-Timings-HOWTO)

## 6.17 Use MS Windows

Some people have attempted to use Windows to see how bus-resources have been set up. Unfortunately, since PnP hardware forgets its bus-resource configuration when powered down, the configuration may not be the same under Linux. For non PnP hardware (or where someone has disabled PnP inside the device by jumpers or Windows software), then using Windows should work OK. Even for PnP, it often turns out to be the same because in many cases both Windows and Linux simply accept what the BIOS has set. But where Windows and/or Linux do the configuring, they may do it differently. So don't count on PnP devices being configured the same.

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