If you try to read FW_LOADER today it speaks of old riddles and unless you have been following development closely you will loose track of what is what. Even the documentation for PREVENT_FIRMWARE_BUILD is a bit fuzzy and how it fits into this big picture.
Give the FW_LOADER kconfig documentation some love with more up to date developments and recommendations. While at it, wrap the FW_LOADER code into its own menu to compartamentalize and make it clearer which components really are part of the FW_LOADER. This should also make it easier to later move these kconfig entries into the firmware_loader/ directory later. This also now recommends using firmwared [0] for folks left needing a uevent handler in userspace for the sysfs firmware fallback mechanis given udev's uevent firmware mechanism was ripped out a while ago. [0] https://github.com/teg/firmwared Signed-off-by: Luis R. Rodriguez <mcg...@kernel.org> --- drivers/base/Kconfig | 165 ++++++++++++++++++++++++++++++++++--------- 1 file changed, 131 insertions(+), 34 deletions(-) diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index 29b0eb452b3a..a4fe86caecca 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -70,39 +70,64 @@ config STANDALONE If unsure, say Y. config PREVENT_FIRMWARE_BUILD - bool "Prevent firmware from being built" + bool "Disable drivers features which enable custom firmware building" 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. + Say yes to disable driver features which enable building a custom + driver firmwar 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 "Userspace firmware loading support" if EXPERT + tristate "Firmware loading facility" 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. + 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 "External firmware blobs to build into the kernel binary" - depends on FW_LOADER + string "Build these firmware blobs into the kernel binary" help - Various drivers in the kernel source tree may require firmware, - which is generally available in your distribution's linux-firmware - package. + 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 preceeded + over firmware lookups using your filesystem over the supported + /lib/firmware paths documented on CONFIG_FW_LOADER. - 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 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() @@ -113,7 +138,7 @@ config EXTRA_FIRMWARE 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. + 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, @@ -130,22 +155,94 @@ config EXTRA_FIRMWARE_DIR looks for the firmware files listed in the EXTRA_FIRMWARE option. config FW_LOADER_USER_HELPER - bool + 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 firwmare is always used first now. + + If the kernel's direct filesystem lookup for firware 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 supressed 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 possibily 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 "Fallback user-helper invocation for firmware loading" - depends on FW_LOADER - select FW_LOADER_USER_HELPER + bool "Force the firmware sysfs fallback mechanism when possible" + depends on 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. + 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 -- 2.17.0
