1 files changed, 117 insertions, 0 deletions

diff --git a/usr/Kconfig b/usr/Kconfig
index bf8e8f15358f..6278f135256d 100644
--- a/usr/Kconfig
+++ b/usr/Kconfig
@@ -99,8 +99,125 @@ config RD_LZ4
           Support loading of a LZ4 encoded initial ramdisk or cpio buffer
           If unsure, say N.
 
+choice
+        prompt "Built-in initramfs compression mode"
+        depends on INITRAMFS_SOURCE!=""
+        optional
+        help
+          This option allows you to decide by which algorithm the builtin
+          initramfs will be compressed.  Several compression algorithms are
+          available, which differ in efficiency, compression and
+          decompression speed.  Compression speed is only relevant
+          when building a kernel.  Decompression speed is relevant at
+          each boot. Also the memory usage during decompression may become
+          relevant on memory constrained systems. This is usually based on the
+          dictionary size of the algorithm with algorithms like XZ and LZMA
+          featuring large dictionary sizes.
+
+          High compression options are mostly useful for users who are
+          low on RAM, since it reduces the memory consumption during
+          boot.
+
+          Keep in mind that your build system needs to provide the appropriate
+          compression tool to compress the generated initram cpio file for
+          embedding.
+
+          If in doubt, select 'None'
+
+config INITRAMFS_COMPRESSION_NONE
+        bool "None"
+        help
+          Do not compress the built-in initramfs at all. This may sound wasteful
+          in space, but, you should be aware that the built-in initramfs will be
+          compressed at a later stage anyways along with the rest of the kernel,
+          on those architectures that support this. However, not compressing the
+          initramfs may lead to slightly higher memory consumption during a
+          short time at boot, while both the cpio image and the unpacked
+          filesystem image will be present in memory simultaneously
+
+config INITRAMFS_COMPRESSION_GZIP
+        bool "Gzip"
+        depends on RD_GZIP
+        help
+          Use the old and well tested gzip compression algorithm. Gzip provides
+          a good balance between compression ratio and decompression speed and
+          has a reasonable compression speed. It is also more likely to be
+          supported by your build system as the gzip tool is present by default
+          on most distros.
+
+config INITRAMFS_COMPRESSION_BZIP2
+        bool "Bzip2"
+        depends on RD_BZIP2
+        help
+          It's compression ratio and speed is intermediate. Decompression speed
+          is slowest among the choices. The initramfs size is about 10% smaller
+          with bzip2, in comparison to gzip. Bzip2 uses a large amount of
+          memory. For modern kernels you will need at least 8MB RAM or more for
+          booting.
+
+          If you choose this, keep in mind that you need to have the bzip2 tool
+          available to be able to compress the initram.
+
+config INITRAMFS_COMPRESSION_LZMA
+        bool "LZMA"
+        depends on RD_LZMA
+        help
+          This algorithm's compression ratio is best but has a large dictionary
+          size which might cause issues in memory constrained systems.
+          Decompression speed is between the other choices. Compression is
+          slowest. The initramfs size is about 33% smaller with LZMA in
+          comparison to gzip.
+
+          If you choose this, keep in mind that you may need to install the xz
+          or lzma tools to be able to compress the initram.
+
+config INITRAMFS_COMPRESSION_XZ
+        bool "XZ"
+        depends on RD_XZ
+        help
+          XZ uses the LZMA2 algorithm and has a large dictionary which may cause
+          problems on memory constrained systems. The initramfs size is about
+          30% smaller with XZ in comparison to gzip. Decompression speed is
+          better than that of bzip2 but worse than gzip and LZO. Compression is
+          slow.
+
+          If you choose this, keep in mind that you may need to install the xz
+          tool to be able to compress the initram.
+
+config INITRAMFS_COMPRESSION_LZO
+        bool "LZO"
+        depends on RD_LZO
+        help
+          It's compression ratio is the second poorest amongst the choices. The
+          kernel size is about 10% bigger than gzip. Despite that, it's
+          decompression speed is the second fastest and it's compression speed
+          is quite fast too.
+
+          If you choose this, keep in mind that you may need to install the lzop
+          tool to be able to compress the initram.
+
+config INITRAMFS_COMPRESSION_LZ4
+        bool "LZ4"
+        depends on RD_LZ4
+        help
+          It's compression ratio is the poorest amongst the choices. The kernel
+          size is about 15% bigger than gzip; however its decompression speed
+          is the fastest.
+
+          If you choose this, keep in mind that most distros don't provide lz4
+          by default which could cause a build failure.
+
+endchoice
+
 config INITRAMFS_COMPRESSION
         string
+        default ""      if INITRAMFS_COMPRESSION_NONE
+        default ".gz"   if INITRAMFS_COMPRESSION_GZIP
+        default ".bz2"  if INITRAMFS_COMPRESSION_BZIP2
+        default ".lzma" if INITRAMFS_COMPRESSION_LZMA
+        default ".xz"   if INITRAMFS_COMPRESSION_XZ
+        default ".lzo"  if INITRAMFS_COMPRESSION_LZO
+        default ".lz4"  if INITRAMFS_COMPRESSION_LZ4
         default ".gz"   if RD_GZIP
         default ".lz4"  if RD_LZ4
         default ".lzo"  if RD_LZO