# SPDX-License-Identifier: GPL-2.0
menu "Generic Driver Options"
config UEVENT_HELPER
bool "Support for uevent helper"
default y
help
The uevent helper program is forked by the kernel for
every uevent.
Before the switch to the netlink-based uevent source, this was
used to hook hotplug scripts into kernel device events. It
usually pointed to a shell script at /sbin/hotplug.
This should not be used today, because usual systems create
many events at bootup or device discovery in a very short time
frame. One forked process per event can create so many processes
that it creates a high system load, or on smaller systems
it is known to create out-of-memory situations during bootup.
config UEVENT_HELPER_PATH
string "path to uevent helper"
depends on UEVENT_HELPER
default ""
help
To disable user space helper program execution at by default
specify an empty string here. This setting can still be altered
via /proc/sys/kernel/hotplug or via /sys/kernel/uevent_helper
later at runtime.
config DEVTMPFS
bool "Maintain a devtmpfs filesystem to mount at /dev"
help
This creates a tmpfs/ramfs filesystem instance early at bootup.
In this filesystem, the kernel driver core maintains device
nodes with their default names and permissions for all
registered devices with an assigned major/minor number.
Userspace can modify the filesystem content as needed, add
symlinks, and apply needed permissions.
It provides a fully functional /dev directory, where usually
udev runs on top, managing permissions and adding meaningful
symlinks.
In very limited environments, it may provide a sufficient
functional /dev without any further help. It also allows simple
rescue systems, and reliably handles dynamic major/minor numbers.
Notice: if CONFIG_TMPFS isn't enabled, the simpler ramfs
file system will be used instead.
config DEVTMPFS_MOUNT
bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
depends on DEVTMPFS
help
This will instruct the kernel to automatically mount the
devtmpfs filesystem at /dev, directly after the kernel has
mounted the root filesystem. The behavior can be overridden
with the commandline parameter: devtmpfs.mount=0|1.
This option does not affect initramfs based booting, here
the devtmpfs filesystem always needs to be mounted manually
after the rootfs is mounted.
With this option enabled, it allows to bring up a system in
rescue mode with init=/bin/sh, even when the /dev directory
on the rootfs is completely empty.
config STANDALONE
bool "Select only drivers that don't need compile-time external firmware"
default y
help
Select this option if you don't have magic firmware for drivers that
need it.
If unsure, say Y.
config PREVENT_FIRMWARE_BUILD
bool "Disable drivers features which enable custom firmware building"
default y
help
Say yes to disable driver features which enable building a custom
driver firmware at kernel build time. These drivers do not use the
kernel firmware API to load firmware (CONFIG_FW_LOADER), instead they
use their own custom loading mechanism. The required firmware is
usually shipped with the driver, building the driver firmware
should only be needed if you have an updated firmware source.
Firmware should not be being built as part of kernel, these days
you should always prevent this and say Y here. There are only two
old drivers which enable building of its firmware at kernel build
time:
o CONFIG_WANXL through CONFIG_WANXL_BUILD_FIRMWARE
o CONFIG_SCSI_AIC79XX through CONFIG_AIC79XX_BUILD_FIRMWARE
menu "Firmware loader"
config FW_LOADER
tristate "Firmware loading facility" if EXPERT
default y
help
This enables the firmware loading facility in the kernel. The kernel
will first look for built-in firmware, if it has any. Next, it will
look for the requested firmware in a series of filesystem paths:
o firmware_class path module parameter or kernel boot param
o /lib/firmware/updates/UTS_RELEASE
o /lib/firmware/updates
o /lib/firmware/UTS_RELEASE
o /lib/firmware
Enabling this feature only increases your kernel image by about
828 bytes, enable this option unless you are certain you don't
need firmware.
You typically want this built-in (=y) but you can also enable this
as a module, in which case the firmware_class module will be built.
You also want to be sure to enable this built-in if you are going to
enable built-in firmware (CONFIG_EXTRA_FIRMWARE).
if FW_LOADER
config EXTRA_FIRMWARE
string "Build named firmware blobs into the kernel binary"
help
Device drivers which require firmware can typically deal with
having the kernel load firmware from the various supported
/lib/firmware/ paths. This option enables you to build into the
kernel firmware files. Built-in firmware searches are preceded
over firmware lookups using your filesystem over the supported
/lib/firmware paths documented on CONFIG_FW_LOADER.
This may be useful for testing or if the firmware is required early on
in boot and cannot rely on the firmware being placed in an initrd or
initramfs.
This option is a string and takes the (space-separated) names of the
firmware files -- the same names that appear in MODULE_FIRMWARE()
and request_firmware() in the source. These files should exist under
the directory specified by the EXTRA_FIRMWARE_DIR option, which is
/lib/firmware by default.
For example, you might set CONFIG_EXTRA_FIRMWARE="usb8388.bin", copy
the usb8388.bin file into /lib/firmware, and build the kernel. Then
any request_firmware("usb8388.bin") will be satisfied internally
inside the kernel without ever looking at your filesystem at runtime.
WARNING: If you include additional firmware files into your binary
kernel image that are not available under the terms of the GPL,
then it may be a violation of the GPL to distribute the resulting
image since it combines both GPL and non-GPL work. You should
consult a lawyer of your own before distributing such an image.
config EXTRA_FIRMWARE_DIR
string "Firmware blobs root directory"
depends on EXTRA_FIRMWARE != ""
default "/lib/firmware"
help
This option controls the directory in which the kernel build system
looks for the firmware files listed in the EXTRA_FIRMWARE option.
config FW_LOADER_USER_HELPER
bool "Enable the firmware sysfs fallback mechanism"
help
This option enables a sysfs loading facility to enable firmware
loading to the kernel through userspace as a fallback mechanism
if and only if the kernel's direct filesystem lookup for the
firmware failed using the different /lib/firmware/ paths, or the
path specified in the firmware_class path module parameter, or the
firmware_class path kernel boot parameter if the firmware_class is
built-in. For details on how to work with the sysfs fallback mechanism
refer to Documentation/driver-api/firmware/fallback-mechanisms.rst.
The direct filesystem lookup for firmware is always used first now.
If the kernel's direct filesystem lookup for firmware fails to find
the requested firmware a sysfs fallback loading facility is made
available and userspace is informed about this through uevents.
The uevent can be suppressed if the driver explicitly requested it,
this is known as the driver using the custom fallback mechanism.
If the custom fallback mechanism is used userspace must always
acknowledge failure to find firmware as the timeout for the fallback
mechanism is disabled, and failed requests will linger forever.
This used to be the default firmware loading facility, and udev used
to listen for uvents to load firmware for the kernel. The firmware
loading facility functionality in udev has been removed, as such it
can no longer be relied upon as a fallback mechanism. Linux no longer
relies on or uses a fallback mechanism in userspace. If you need to
rely on one refer to the permissively licensed firmwared:
https://github.com/teg/firmwared
Since this was the default firmware loading facility at one point,
old userspace may exist which relies upon it, and as such this
mechanism can never be removed from the kernel.
You should only enable this functionality if you are certain you
require a fallback mechanism and have a userspace mechanism ready to
load firmware in case it is not found. One main reason for this may
be if you have drivers which require firmware built-in and for
whatever reason cannot place the required firmware in initramfs.
Another reason kernels may have this feature enabled is to support a
driver which explicitly relies on this fallback mechanism. Only two
drivers need this today:
o CONFIG_LEDS_LP55XX_COMMON
o CONFIG_DELL_RBU
Outside of supporting the above drivers, another reason for needing
this may be that your firmware resides outside of the paths the kernel
looks for and cannot possibly be specified using the firmware_class
path module parameter or kernel firmware_class path boot parameter
if firmware_class is built-in.
A modern use case may be to temporarily mount a custom partition
during provisioning which is only accessible to userspace, and then
to use it to look for and fetch the required firmware. Such type of
driver functionality may not even ever be desirable upstream by
vendors, and as such is only required to be supported as an interface
for provisioning. Since udev's firmware loading facility has been
removed you can use firmwared or a fork of it to customize how you
want to load firmware based on uevents issued.
Enabling this option will increase your kernel image size by about
13436 bytes.
If you are unsure about this, say N here, unless you are Linux
distribution and need to support the above two drivers, or you are
certain you need to support some really custom firmware loading
facility in userspace.
config FW_LOADER_USER_HELPER_FALLBACK
bool "Force the firmware sysfs fallback mechanism when possible"
depends on FW_LOADER_USER_HELPER
help
Enabling this option forces a sysfs userspace fallback mechanism
to be used for all firmware requests which explicitly do not disable a
a fallback mechanism. Firmware calls which do prohibit a fallback
mechanism is request_firmware_direct(). This option is kept for
backward compatibility purposes given this precise mechanism can also
be enabled by setting the proc sysctl value to true:
/proc/sys/kernel/firmware_config/force_sysfs_fallback
If you are unsure about this, say N here.
endif # FW_LOADER
endmenu
config WANT_DEV_COREDUMP
bool
help
Drivers should "select" this option if they desire to use the
device coredump mechanism.
config ALLOW_DEV_COREDUMP
bool "Allow device coredump" if EXPERT
default y
help
This option controls if the device coredump mechanism is available or
not; if disabled, the mechanism will be omitted even if drivers that
can use it are enabled.
Say 'N' for more sensitive systems or systems that don't want
to ever access the information to not have the code, nor keep any
data.
If unsure, say Y.
config DEV_COREDUMP
bool
default y if WANT_DEV_COREDUMP
depends on ALLOW_DEV_COREDUMP
config DEBUG_DRIVER
bool "Driver Core verbose debug messages"
depends on DEBUG_KERNEL
help
Say Y here if you want the Driver core to produce a bunch of
debug messages to the system log. Select this if you are having a
problem with the driver core and want to see more of what is
going on.
If you are unsure about this, say N here.
config DEBUG_DEVRES
bool "Managed device resources verbose debug messages"
depends on DEBUG_KERNEL
help
This option enables kernel parameter devres.log. If set to
non-zero, devres debug messages are printed. Select this if
you are having a problem with devres or want to debug
resource management for a managed device. devres.log can be
switched on and off from sysfs node.
If you are unsure about this, Say N here.
config DEBUG_TEST_DRIVER_REMOVE
bool "Test driver remove calls during probe (UNSTABLE)"
depends on DEBUG_KERNEL
help
Say Y here if you want the Driver core to test driver remove functions
by calling probe, remove, probe. This tests the remove path without
having to unbind the driver or unload the driver module.
This option is expected to find errors and may render your system
unusable. You should say N here unless you are explicitly looking to
test this functionality.
source "drivers/base/test/Kconfig"
config SYS_HYPERVISOR
bool
default n
config GENERIC_CPU_DEVICES
bool
default n
config GENERIC_CPU_AUTOPROBE
bool
config GENERIC_CPU_VULNERABILITIES
bool
config SOC_BUS
bool
select GLOB
source "drivers/base/regmap/Kconfig"
config DMA_SHARED_BUFFER
bool
default n
select ANON_INODES
select IRQ_WORK
help
This option enables the framework for buffer-sharing between
multiple drivers. A buffer is associated with a file using driver
APIs extension; the file's descriptor can then be passed on to other
driver.
config DMA_FENCE_TRACE
bool "Enable verbose DMA_FENCE_TRACE messages"
depends on DMA_SHARED_BUFFER
help
Enable the DMA_FENCE_TRACE printks. This will add extra
spam to the console log, but will make it easier to diagnose
lockup related problems for dma-buffers shared across multiple
devices.
config DMA_CMA
bool "DMA Contiguous Memory Allocator"
depends on HAVE_DMA_CONTIGUOUS && CMA
help
This enables the Contiguous Memory Allocator which allows drivers
to allocate big physically-contiguous blocks of memory for use with
hardware components that do not support I/O map nor scatter-gather.
You can disable CMA by specifying "cma=0" on the kernel's command
line.
For more information see <include/linux/dma-contiguous.h>.
If unsure, say "n".
if DMA_CMA
comment "Default contiguous memory area size:"
config CMA_SIZE_MBYTES
int "Size in Mega Bytes"
depends on !CMA_SIZE_SEL_PERCENTAGE
default 0 if X86
default 16
help
Defines the size (in MiB) of the default memory area for Contiguous
Memory Allocator. If the size of 0 is selected, CMA is disabled by
default, but it can be enabled by passing cma=size[MG] to the kernel.
config CMA_SIZE_PERCENTAGE
int "Percentage of total memory"
depends on !CMA_SIZE_SEL_MBYTES
default 0 if X86
default 10
help
Defines the size of the default memory area for Contiguous Memory
Allocator as a percentage of the total memory in the system.
If 0 percent is selected, CMA is disabled by default, but it can be
enabled by passing cma=size[MG] to the kernel.
choice
prompt "Selected region size"
default CMA_SIZE_SEL_MBYTES
config CMA_SIZE_SEL_MBYTES
bool "Use mega bytes value only"
config CMA_SIZE_SEL_PERCENTAGE
bool "Use percentage value only"
config CMA_SIZE_SEL_MIN
bool "Use lower value (minimum)"
config CMA_SIZE_SEL_MAX
bool "Use higher value (maximum)"
endchoice
config CMA_ALIGNMENT
int "Maximum PAGE_SIZE order of alignment for contiguous buffers"
range 4 12
default 8
help
DMA mapping framework by default aligns all buffers to the smallest
PAGE_SIZE order which is greater than or equal to the requested buffer
size. This works well for buffers up to a few hundreds kilobytes, but
for larger buffers it just a memory waste. With this parameter you can
specify the maximum PAGE_SIZE order for contiguous buffers. Larger
buffers will be aligned only to this specified order. The order is
expressed as a power of two multiplied by the PAGE_SIZE.
For example, if your system defaults to 4KiB pages, the order value
of 8 means that the buffers will be aligned up to 1MiB only.
If unsure, leave the default value "8".
endif
config GENERIC_ARCH_TOPOLOGY
bool
help
Enable support for architectures common topology code: e.g., parsing
CPU capacity information from DT, usage of such information for
appropriate scaling, sysfs interface for changing capacity values at
runtime.
endmenu
