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Diffstat (limited to 'Documentation/devicetree/booting-without-of.txt')
| -rw-r--r-- | Documentation/devicetree/booting-without-of.txt | 54 |
1 files changed, 47 insertions, 7 deletions
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt index 55fd2623445..7c1329de059 100644 --- a/Documentation/devicetree/booting-without-of.txt +++ b/Documentation/devicetree/booting-without-of.txt @@ -12,8 +12,9 @@ Table of Contents ================= I - Introduction - 1) Entry point for arch/powerpc - 2) Entry point for arch/x86 + 1) Entry point for arch/arm + 2) Entry point for arch/powerpc + 3) Entry point for arch/x86 II - The DT block format 1) Header @@ -138,7 +139,7 @@ and properties to be present. This will be described in detail in section III, but, for example, the kernel does not require you to create a node for every PCI device in the system. It is a requirement to have a node for PCI host bridges in order to provide interrupt -routing informations and memory/IO ranges, among others. It is also +routing information and memory/IO ranges, among others. It is also recommended to define nodes for on chip devices and other buses that don't specifically fit in an existing OF specification. This creates a great flexibility in the way the kernel can then probe those and match @@ -148,7 +149,46 @@ upgrades without significantly impacting the kernel code or cluttering it with special cases. -1) Entry point for arch/powerpc +1) Entry point for arch/arm +--------------------------- + + There is one single entry point to the kernel, at the start + of the kernel image. That entry point supports two calling + conventions. A summary of the interface is described here. A full + description of the boot requirements is documented in + Documentation/arm/Booting + + a) ATAGS interface. Minimal information is passed from firmware + to the kernel with a tagged list of predefined parameters. + + r0 : 0 + + r1 : Machine type number + + r2 : Physical address of tagged list in system RAM + + b) Entry with a flattened device-tree block. Firmware loads the + physical address of the flattened device tree block (dtb) into r2, + r1 is not used, but it is considered good practise to use a valid + machine number as described in Documentation/arm/Booting. + + r0 : 0 + + r1 : Valid machine type number. When using a device tree, + a single machine type number will often be assigned to + represent a class or family of SoCs. + + r2 : physical pointer to the device-tree block + (defined in chapter II) in RAM. Device tree can be located + anywhere in system RAM, but it should be aligned on a 64 bit + boundary. + + The kernel will differentiate between ATAGS and device tree booting by + reading the memory pointed to by r2 and looking for either the flattened + device tree block magic value (0xd00dfeed) or the ATAG_CORE value at + offset 0x4 from r2 (0x54410001). + +2) Entry point for arch/powerpc ------------------------------- There is one single entry point to the kernel, at the start @@ -226,7 +266,7 @@ it with special cases. cannot support both configurations with Book E and configurations with classic Powerpc architectures. -2) Entry point for arch/x86 +3) Entry point for arch/x86 ------------------------------- There is one single 32bit entry point to the kernel at code32_start, @@ -385,7 +425,7 @@ struct boot_param_header { among others, by kexec. If you are on an SMP system, this value should match the content of the "reg" property of the CPU node in the device-tree corresponding to the CPU calling the kernel entry - point (see further chapters for more informations on the required + point (see further chapters for more information on the required device-tree contents) - size_dt_strings @@ -553,7 +593,7 @@ looks like in practice. This tree is almost a minimal tree. It pretty much contains the minimal set of required nodes and properties to boot a linux kernel; -that is, some basic model informations at the root, the CPUs, and the +that is, some basic model information at the root, the CPUs, and the physical memory layout. It also includes misc information passed through /chosen, like in this example, the platform type (mandatory) and the kernel command line arguments (optional). |