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Linux 3.7 Kernel To Support Multiple ARM Platforms
hypnosec writes with news that the Linux 3.7 kernel will support multiple ARM-based System on Chip platforms (Git commit page), writing "Up until now there has been a separate Linux kernel build for each of the ARM platforms or SoCs, which is one of the several problems when it comes to ARM based Linux. The merging of ARM multi-platform support into Linux 3.7 will put an end to this problem, enabling the new kernel to not only target multiple platforms but also be more in line with its x86 counterpart."
It's called device tree (DT).
The basic infrastructure for supporting bcm2835 (the board used by raspberry pi) was just added a few days ago [1], so maybe 3.7 won't be fully functional on the pi, but it's getting there, I believe/hope.
[1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=11801e9de26992d37cb869cc74f389b6a7677e0e
Those are different ARM based SoCs ("System on a chip"). The problem with the ARM platform is that ARM is not really a platform: The unifying aspect is the line of CPUs in the chip, but the SoCs come with different sets of peripherals. Even simple things like what GPIO (General Purpose IO) is connected to what LED or other function require a completely separate hardware configuration compiled into the kernel. On a PC, the kernel uses the BIOS and self-describing hardware to set everything up and choose the right drivers. No such thing exists on ARM. The kernel has to be told manually what's where. That's why you can't currently take a kernel which is compiled for one ARM SoC and use it on a different kind of ARM SoC. You're lucky if you can use the same kernel on the same ARM SoC in a different device that just happens to have everything wired up slightly differently. You may find that the GPIO that turns on the power LED on one system turns off USB power on another system. Then you need to patch the kernel or, if you want to have mainline support, register a new arc number and have yet another configuration added to the kernel. It's a fucking mess.
In plain English, an ARM processor isn't a chip you can go out and buy from ARM Ltd. It's a processor design (or rather a family of processor designs) you can license from ARM Ltd, re-engineer it to suit your needs if you so choose then fabricate.
If you want a ready-to-go chip, you have to buy it from someone else who's already done that. Broadcom have done so, and it's one of their chips in the Raspberry Pi, but so have lots of other companies.
As a result, there's a whole lot of subtly different variants out there. Not all of them are 100% binary compatible with each other. I haven't been able to find out exactly which variant is used in the raspberry pi.