Linux v4.20-rc4 - drivers/base/Kconfig
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menu "Generic Driver Options"
bool "Support for uevent helper"
The uevent helper program is forked by the kernel for
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.
string "path to uevent helper"
depends on UEVENT_HELPER
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.
bool "Maintain a devtmpfs filesystem to mount at /dev"
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
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.
bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
depends on DEVTMPFS
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.
bool "Select only drivers that don't need compile-time external firmware"
Select this option if you don't have magic firmware for drivers that
If unsure, say Y.
bool "Disable drivers features which enable custom firmware building"
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
o CONFIG_WANXL through CONFIG_WANXL_BUILD_FIRMWARE
o CONFIG_SCSI_AIC79XX through CONFIG_AIC79XX_BUILD_FIRMWARE
Drivers should "select" this option if they desire to use the
device coredump mechanism.
bool "Allow device coredump" if EXPERT
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
If unsure, say Y.
default y if WANT_DEV_COREDUMP
depends on ALLOW_DEV_COREDUMP
bool "Driver Core verbose debug messages"
depends on DEBUG_KERNEL
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
If you are unsure about this, say N here.
bool "Managed device resources verbose debug messages"
depends on DEBUG_KERNEL
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.
bool "Test driver remove calls during probe (UNSTABLE)"
depends on DEBUG_KERNEL
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.
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
bool "Enable verbose DMA_FENCE_TRACE messages"
depends on DMA_SHARED_BUFFER
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
bool "DMA Contiguous Memory Allocator"
depends on HAVE_DMA_CONTIGUOUS && CMA
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
For more information see <include/linux/dma-contiguous.h>.
If unsure, say "n".
comment "Default contiguous memory area size:"
int "Size in Mega Bytes"
depends on !CMA_SIZE_SEL_PERCENTAGE
default 0 if X86
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.
int "Percentage of total memory"
depends on !CMA_SIZE_SEL_MBYTES
default 0 if X86
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.
prompt "Selected region size"
bool "Use mega bytes value only"
bool "Use percentage value only"
bool "Use lower value (minimum)"
bool "Use higher value (maximum)"
int "Maximum PAGE_SIZE order of alignment for contiguous buffers"
range 4 12
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".
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