Question

I would like to support two similar hardware platforms with one embedded Linux kernel. Does the kernel support multiple struct machine_desc structures? Instances of this structure are usually defined by using the MACHINE_START and MACHINE_END macros in the board’s C definition file.

There is a mechanism to pass the MACH_TYPE from the bootloader to the kernel so it seems to make sense that the kernel can support multiple machines. Does anything special need to be done?

Answer 1

I spent some time looking at the kernel code (version 2.6.33) and the ARM architecture supports multiple machines in the same kernel. However I am not sure if other architectures do. Here’s how it works

1. For each board type to be supported by the kernel, the corresponding CONFIG_MACH_TYPE_* values need to be set in the configuration file. When built, the kernel will then generate the all the machine macros based on the version of mach-types included with the source. The source code for machine definitions will also be compiled into the kernel.
2. When started the bootloader then needs to put the corresponding machine type number (i.e. the number in the last column of mach-types) in register r1 before starting the kernel.
3. During initialization the kernel passes the machine type number from register r1 to __lookup_machine_type to find the machine definition and initializes the board.