path: root/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 "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