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- ========================
- Direct filesystem lookup
- ========================
- Direct filesystem lookup is the most common form of firmware lookup performed
- by the kernel. The kernel looks for the firmware directly on the root
- filesystem in the paths documented in the section 'Firmware search paths'.
- The filesystem lookup is implemented in fw_get_filesystem_firmware(), it
- uses common core kernel file loader facility kernel_read_file_from_path().
- The max path allowed is PATH_MAX -- currently this is 4096 characters.
- It is recommended you keep /lib/firmware paths on your root filesystem,
- avoid having a separate partition for them in order to avoid possible
- races with lookups and avoid uses of the custom fallback mechanisms
- documented below.
- Firmware and initramfs
- ----------------------
- Drivers which are built-in to the kernel should have the firmware integrated
- also as part of the initramfs used to boot the kernel given that otherwise
- a race is possible with loading the driver and the real rootfs not yet being
- available. Stuffing the firmware into initramfs resolves this race issue,
- however note that using initrd does not suffice to address the same race.
- There are circumstances that justify not wanting to include firmware into
- initramfs, such as dealing with large firmware files for the
- remote-proc subsystem. For such cases using a userspace fallback mechanism
- is currently the only viable solution as only userspace can know for sure
- when the real rootfs is ready and mounted.
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