linux_kernel/drivers/base/Kconfig

# 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 "Prevent firmware from being built"
	default y
	help
	  Say yes to avoid building firmware. Firmware is usually shipped
	  with the driver and only when updating the firmware should a
	  rebuild be made.
	  If unsure, say Y here.

config FW_LOADER
	tristate "Userspace firmware loading support" if EXPERT
	default y
	---help---
	  This option is provided for the case where none of the in-tree modules
	  require userspace firmware loading support, but a module built
	  out-of-tree does.

config EXTRA_FIRMWARE
	string "External firmware blobs to build into the kernel binary"
	depends on FW_LOADER
	help
	  Various drivers in the kernel source tree may require firmware,
	  which is generally available in your distribution's linux-firmware
	  package.

	  The linux-firmware package should install firmware into
	  /lib/firmware/ on your system, so they can be loaded by userspace
	  helpers on request.

	  This option allows firmware to be built into the kernel for the case
	  where the user either cannot or doesn't want to provide it from
	  userspace at runtime (for example, when the firmware in question is
	  required for accessing the boot device, and the user doesn't want to
	  use an initrd).

	  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
	  without needing to call out to userspace.

	  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

config FW_LOADER_USER_HELPER_FALLBACK
	bool "Fallback user-helper invocation for firmware loading"
	depends on FW_LOADER
	select FW_LOADER_USER_HELPER
	help
	  This option enables / disables the invocation of user-helper
	  (e.g. udev) for loading firmware files as a fallback after the
	  direct file loading in kernel fails.  The user-mode helper is
	  no longer required unless you have a special firmware file that
	  resides in a non-standard path. Moreover, the udev support has
	  been deprecated upstream.

	  If you are unsure about this, say N here.

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