ref-manual/variables: document the FIRMWARE_COMPRESSION variable

Added in oecore after the 20241017 update.

(From yocto-docs rev: 9073f575f169ab545198d82b69cca5f9e3db152f)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index b31abeced4..21c4c78873 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -3038,6 +3038,16 @@ system and gives an overview of their function and contents.
       tables, examine the existing ``fs-perms.txt``,
       ``fs-perms-volatile-log.txt`` and ``fs-perms-volatile-tmp.txt`` files.
 
+   :term:`FIRMWARE_COMPRESSION`
+      The :term:`FIRMWARE_COMPRESSION` allows compressing the firmware provided
+      by the ``linux-firmware`` recipe. The default value of this variable is an
+      empty string (no compression), and the possible values it can take are
+      ``xz`` and ``zst``. This can allow significant disk space savings.
+
+      For this to work, the Linux Kernel requires the
+      ``CONFIG_FW_LOADER_COMPRESS_XZ`` or ``CONFIG_FW_LOADER_COMPRESS_ZSTD``
+      configuration options to be set.
+
    :term:`FIT_ADDRESS_CELLS`
       Specifies the value of the ``#address-cells`` value for the
       description of the FIT image.