On Tue, May 8, 2018 at 11:12 AM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> wrote: > If you try to read FW_LOADER today it speaks of old riddles and > unless you have been following development closely you will loose Typo: lose > 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 Typo: compartmentalize > 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 <mcgrof@xxxxxxxxxx> > --- > 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 Typo: firmware > + 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" Maybe "Build named firmware blobs ..." "these" took me a while to figure out. > 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 Typo: preceded > + 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. Typo: firmware > + > + 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: Typo: firmware > + > + 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 > -Kees -- Kees Cook Pixel Security
