Linux kernel drivers list

Device Drivers¶

See the kerneldoc for the struct device_driver.

Allocation¶

Device drivers are statically allocated structures. Though there may be multiple devices in a system that a driver supports, struct device_driver represents the driver as a whole (not a particular device instance).

Initialization¶

The driver must initialize at least the name and bus fields. It should also initialize the devclass field (when it arrives), so it may obtain the proper linkage internally. It should also initialize as many of the callbacks as possible, though each is optional.

Declaration¶

As stated above, struct device_driver objects are statically allocated. Below is an example declaration of the eepro100 driver. This declaration is hypothetical only; it relies on the driver being converted completely to the new model:

Most drivers will not be able to be converted completely to the new model because the bus they belong to has a bus-specific structure with bus-specific fields that cannot be generalized.

The most common example of this are device ID structures. A driver typically defines an array of device IDs that it supports. The format of these structures and the semantics for comparing device IDs are completely bus-specific. Defining them as bus-specific entities would sacrifice type-safety, so we keep bus-specific structures around.

Bus-specific drivers should include a generic struct device_driver in the definition of the bus-specific driver. Like this:

A definition that included bus-specific fields would look like (using the eepro100 driver again):

Some may find the syntax of embedded struct initialization awkward or even a bit ugly. So far, it’s the best way we’ve found to do what we want…

Registration¶

The driver registers the structure on startup. For drivers that have no bus-specific fields (i.e. don’t have a bus-specific driver structure), they would use driver_register and pass a pointer to their struct device_driver object.

Most drivers, however, will have a bus-specific structure and will need to register with the bus using something like pci_driver_register.

It is important that drivers register their driver structure as early as possible. Registration with the core initializes several fields in the struct device_driver object, including the reference count and the lock. These fields are assumed to be valid at all times and may be used by the device model core or the bus driver.

Transition Bus Drivers¶

By defining wrapper functions, the transition to the new model can be made easier. Drivers can ignore the generic structure altogether and let the bus wrapper fill in the fields. For the callbacks, the bus can define generic callbacks that forward the call to the bus-specific callbacks of the drivers.

This solution is intended to be only temporary. In order to get class information in the driver, the drivers must be modified anyway. Since converting drivers to the new model should reduce some infrastructural complexity and code size, it is recommended that they are converted as class information is added.

Access¶

Once the object has been registered, it may access the common fields of the object, like the lock and the list of devices:

The devices field is a list of all the devices that have been bound to the driver. The LDM core provides a helper function to operate on all the devices a driver controls. This helper locks the driver on each node access, and does proper reference counting on each device as it accesses it.

sysfs¶

When a driver is registered, a sysfs directory is created in its bus’s directory. In this directory, the driver can export an interface to userspace to control operation of the driver on a global basis; e.g. toggling debugging output in the driver.

A future feature of this directory will be a ‘devices’ directory. This directory will contain symlinks to the directories of devices it supports.

Callbacks¶

The probe() entry is called in task context, with the bus’s rwsem locked and the driver partially bound to the device. Drivers commonly use container_of() to convert “dev” to a bus-specific type, both in probe() and other routines. That type often provides device resource data, such as pci_dev.resource[] or platform_device.resources, which is used in addition to dev->platform_data to initialize the driver.

This callback holds the driver-specific logic to bind the driver to a given device. That includes verifying that the device is present, that it’s a version the driver can handle, that driver data structures can be allocated and initialized, and that any hardware can be initialized. Drivers often store a pointer to their state with dev_set_drvdata(). When the driver has successfully bound itself to that device, then probe() returns zero and the driver model code will finish its part of binding the driver to that device.

A driver’s probe() may return a negative errno value to indicate that the driver did not bind to this device, in which case it should have released all resources it allocated.

Optionally, probe() may return -EPROBE_DEFER if the driver depends on resources that are not yet available (e.g., supplied by a driver that hasn’t initialized yet). The driver core will put the device onto the deferred probe list and will try to call it again later. If a driver must defer, it should return -EPROBE_DEFER as early as possible to reduce the amount of time spent on setup work that will need to be unwound and reexecuted at a later time.

-EPROBE_DEFER must not be returned if probe() has already created child devices, even if those child devices are removed again in a cleanup path. If -EPROBE_DEFER is returned after a child device has been registered, it may result in an infinite loop of .probe() calls to the same driver.

sync_state is called only once for a device. It’s called when all the consumer devices of the device have successfully probed. The list of consumers of the device is obtained by looking at the device links connecting that device to its consumer devices.

The first attempt to call sync_state() is made during late_initcall_sync() to give firmware and drivers time to link devices to each other. During the first attempt at calling sync_state(), if all the consumers of the device at that point in time have already probed successfully, sync_state() is called right away. If there are no consumers of the device during the first attempt, that too is considered as “all consumers of the device have probed” and sync_state() is called right away.

If during the first attempt at calling sync_state() for a device, there are still consumers that haven’t probed successfully, the sync_state() call is postponed and reattempted in the future only when one or more consumers of the device probe successfully. If during the reattempt, the driver core finds that there are one or more consumers of the device that haven’t probed yet, then sync_state() call is postponed again.

A typical use case for sync_state() is to have the kernel cleanly take over management of devices from the bootloader. For example, if a device is left on and at a particular hardware configuration by the bootloader, the device’s driver might need to keep the device in the boot configuration until all the consumers of the device have probed. Once all the consumers of the device have probed, the device’s driver can synchronize the hardware state of the device to match the aggregated software state requested by all the consumers. Hence the name sync_state().

While obvious examples of resources that can benefit from sync_state() include resources such as regulator, sync_state() can also be useful for complex resources like IOMMUs. For example, IOMMUs with multiple consumers (devices whose addresses are remapped by the IOMMU) might need to keep their mappings fixed at (or additive to) the boot configuration until all its consumers have probed.

While the typical use case for sync_state() is to have the kernel cleanly take over management of devices from the bootloader, the usage of sync_state() is not restricted to that. Use it whenever it makes sense to take an action after all the consumers of a device have probed:

remove is called to unbind a driver from a device. This may be called if a device is physically removed from the system, if the driver module is being unloaded, during a reboot sequence, or in other cases.

It is up to the driver to determine if the device is present or not. It should free any resources allocated specifically for the device; i.e. anything in the device’s driver_data field.

If the device is still present, it should quiesce the device and place it into a supported low-power state.

suspend is called to put the device in a low power state.

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Linux: Find out what kernel drivers (modules) are loaded

lsmod command

You need to use lsmod command to show the status of modules in the Linux Kernel. Simply type the lsmod at a shell prompt to list all loaded modules:
$ lsmod
Sample outputs:

Get more information about the driver

To get more information about specific driver use modinfo command. The syntax is:
modinfo < driver-name >
To see information about a Linux Kernel module called e1000, enter:
$ modinfo e1000
Sample outputs:

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See modinfo and lsmod man pages for more info.

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LKDDb: Linux Kernel Driver DataBase

what Linux drivers are for me?

About LKDDb

LKDDb is an attempt to build a comprensive database of hardware and protocols know by Linux kernels. The driver database includes numeric identifiers of hardware, the kernel configuration menu needed to build the driver and the driver filename. The database is build automagically from kernel sources, so it is very easy to have always the database updated.

There exists two versions: text based database, to be processed automatically (see lkddb.list below), and the web LKDDb version, which includes also text and hardware strings from kernel and other databases.

Automagical Kernel Configuration

The automatic kernel configuration is an obvious application of the driver database. It combines an hardware detection, that could be easy performed checking buses in /sys/bus .

The Automagical Kernel Configuration has an own AutoKernConf project page.

Important news about the project:

• 2007-11-22: API changes. Now I use lkddb.list with different format.
• 2007-11-13: web lkddb of a browsable and human readable version of the database
• 2007-11-08: code clean-up, better detections, finished the format page. Renamed the database to lkddb.data
• 2007-11-01: add module name, configuration as virtual data
• 2007-10-29: created this page
• 2007-10-28: annonced the project in the lkml

• 2007-11-22: add ‘zorro’ support.
• 2007-11-12: better (general) regex, so huge increment (three times) of USB devices (and also some more PCI devices).
• 2007-11-12: add TURBOchannel (tc) detection

Getting the database

The database is a text file, which contains: sub system, sub system specific hardware data, kernel configurations and kernel driver file that contain such probe. Usually the system specific hardware data is in form of mask, and list only fields that are really checked by the kernel. Detailed information are available in lkddb format page.

The latest versions is in file lkddb.list on sources/lkddb/ directory.

Actually the LKDDb contains probes for the subsytems:

• PCI bus devices
• USB bus devices
• IEEE1394 devices
• s390 CCW devices
• s390 AP bus devices
• ACPI devices
• Plug’N Play (PnP) devices (on ISA bus)
• Plug’N Play (PnP) devices (on ISA bus) alternate kernel detection
• SERIO
• OF
• VIO
• PCMCIA bus devices
• input
• EISA bus devices
• parisc specific devices
• SDIO
• SBB (Sonics Silicon Backplane) bus devices
• virtio (virtual I/O)
• TC (TURBOchannel)
• Zorro
• I2C
• Filesystem (only the names, no harddisk detection)
• modules (virtual probes): map module name with configuration

There also some statistics on total probes, and probes per subsystem.

Getting the lkddb.list generator

The program ( build-lkddb.py and four short modules: devicetables.py (definition of probes), utils.py (main support routines), kbuildparser.py (support for configuration and makefiles), srcparser.py (expand macro)) is a python script, distributed with the GNU GPL v2. It was designed with a lot of euristic on how the hardware is coded in Linux kernel, but it should be pretty accurate, and designed to be quite fast (it take nearly 2 minutes, with warm cache on my computer). Additionally, the program web-lkddb-gen.py will build the online version of lkddb.

The sources are placed in the sources/lkddb-sources/ directory.

Usage:

The first argument is the top directory of kernel source tree. Eventually you can restrict the subdirectories to be parsed, adding as extra arguments these directories (Note: anyway it will parse the whole include/ directories).

The program will write the database to lkddb.list , and a lot of diagnostic message to the console (which I use to improve euristic detection).

Slides

I’ve done a presentation at a Open Source Jam in Google Zurich:

History

A long time ago (in 2000), to remove some Empire code, the former kbuild team designed a new way to build and configure the kernel. The third (and minor) task was to add an autoconfig target to the build system. I took the autoconfiguration part. Then was flames, flames and flame (maybe someone remember about CML2 and the Aunt Tillie. So the new make and the new CML2 was rejected, and because my part was dependent to the other two sub project (and to have a simpler life), I hibernate the project.

In late 2007, I restored the project, rewriting and publishing some part that was never finished. Atually I works more on the driver database, because I find that automatic configuration is a more problematic field: what should be the target configuration? In direction of perfection, so minimal, or in direction of optimal, so removing only surelly unneeded drivers?.

So I split the project in two, allowing external programs to use the database.

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