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diff --git a/Documentation/powerpc/bootwrapper.rst b/Documentation/powerpc/bootwrapper.rst deleted file mode 100644 index cdfa2bc842..0000000000 --- a/Documentation/powerpc/bootwrapper.rst +++ /dev/null @@ -1,131 +0,0 @@ -======================== -The PowerPC boot wrapper -======================== - -Copyright (C) Secret Lab Technologies Ltd. - -PowerPC image targets compresses and wraps the kernel image (vmlinux) with -a boot wrapper to make it usable by the system firmware. There is no -standard PowerPC firmware interface, so the boot wrapper is designed to -be adaptable for each kind of image that needs to be built. - -The boot wrapper can be found in the arch/powerpc/boot/ directory. The -Makefile in that directory has targets for all the available image types. -The different image types are used to support all of the various firmware -interfaces found on PowerPC platforms. OpenFirmware is the most commonly -used firmware type on general purpose PowerPC systems from Apple, IBM and -others. U-Boot is typically found on embedded PowerPC hardware, but there -are a handful of other firmware implementations which are also popular. Each -firmware interface requires a different image format. - -The boot wrapper is built from the makefile in arch/powerpc/boot/Makefile and -it uses the wrapper script (arch/powerpc/boot/wrapper) to generate target -image. The details of the build system is discussed in the next section. -Currently, the following image format targets exist: - - ==================== ======================================================== - cuImage.%: Backwards compatible uImage for older version of - U-Boot (for versions that don't understand the device - tree). This image embeds a device tree blob inside - the image. The boot wrapper, kernel and device tree - are all embedded inside the U-Boot uImage file format - with boot wrapper code that extracts data from the old - bd_info structure and loads the data into the device - tree before jumping into the kernel. - - Because of the series of #ifdefs found in the - bd_info structure used in the old U-Boot interfaces, - cuImages are platform specific. Each specific - U-Boot platform has a different platform init file - which populates the embedded device tree with data - from the platform specific bd_info file. The platform - specific cuImage platform init code can be found in - `arch/powerpc/boot/cuboot.*.c`. Selection of the correct - cuImage init code for a specific board can be found in - the wrapper structure. - - dtbImage.%: Similar to zImage, except device tree blob is embedded - inside the image instead of provided by firmware. The - output image file can be either an elf file or a flat - binary depending on the platform. - - dtbImages are used on systems which do not have an - interface for passing a device tree directly. - dtbImages are similar to simpleImages except that - dtbImages have platform specific code for extracting - data from the board firmware, but simpleImages do not - talk to the firmware at all. - - PlayStation 3 support uses dtbImage. So do Embedded - Planet boards using the PlanetCore firmware. Board - specific initialization code is typically found in a - file named arch/powerpc/boot/<platform>.c; but this - can be overridden by the wrapper script. - - simpleImage.%: Firmware independent compressed image that does not - depend on any particular firmware interface and embeds - a device tree blob. This image is a flat binary that - can be loaded to any location in RAM and jumped to. - Firmware cannot pass any configuration data to the - kernel with this image type and it depends entirely on - the embedded device tree for all information. - - treeImage.%; Image format for used with OpenBIOS firmware found - on some ppc4xx hardware. This image embeds a device - tree blob inside the image. - - uImage: Native image format used by U-Boot. The uImage target - does not add any boot code. It just wraps a compressed - vmlinux in the uImage data structure. This image - requires a version of U-Boot that is able to pass - a device tree to the kernel at boot. If using an older - version of U-Boot, then you need to use a cuImage - instead. - - zImage.%: Image format which does not embed a device tree. - Used by OpenFirmware and other firmware interfaces - which are able to supply a device tree. This image - expects firmware to provide the device tree at boot. - Typically, if you have general purpose PowerPC - hardware then you want this image format. - ==================== ======================================================== - -Image types which embed a device tree blob (simpleImage, dtbImage, treeImage, -and cuImage) all generate the device tree blob from a file in the -arch/powerpc/boot/dts/ directory. The Makefile selects the correct device -tree source based on the name of the target. Therefore, if the kernel is -built with 'make treeImage.walnut', then the build system will use -arch/powerpc/boot/dts/walnut.dts to build treeImage.walnut. - -Two special targets called 'zImage' and 'zImage.initrd' also exist. These -targets build all the default images as selected by the kernel configuration. -Default images are selected by the boot wrapper Makefile -(arch/powerpc/boot/Makefile) by adding targets to the $image-y variable. Look -at the Makefile to see which default image targets are available. - -How it is built ---------------- -arch/powerpc is designed to support multiplatform kernels, which means -that a single vmlinux image can be booted on many different target boards. -It also means that the boot wrapper must be able to wrap for many kinds of -images on a single build. The design decision was made to not use any -conditional compilation code (#ifdef, etc) in the boot wrapper source code. -All of the boot wrapper pieces are buildable at any time regardless of the -kernel configuration. Building all the wrapper bits on every kernel build -also ensures that obscure parts of the wrapper are at the very least compile -tested in a large variety of environments. - -The wrapper is adapted for different image types at link time by linking in -just the wrapper bits that are appropriate for the image type. The 'wrapper -script' (found in arch/powerpc/boot/wrapper) is called by the Makefile and -is responsible for selecting the correct wrapper bits for the image type. -The arguments are well documented in the script's comment block, so they -are not repeated here. However, it is worth mentioning that the script -uses the -p (platform) argument as the main method of deciding which wrapper -bits to compile in. Look for the large 'case "$platform" in' block in the -middle of the script. This is also the place where platform specific fixups -can be selected by changing the link order. - -In particular, care should be taken when working with cuImages. cuImage -wrapper bits are very board specific and care should be taken to make sure -the target you are trying to build is supported by the wrapper bits. |