# 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 . 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