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ArsTechnica

Next Linux kernel release supports more ARMs with less code
by Sean Gallagher - Oct 5 2012, 5:15pm EDT

A new coding effort recently folded into the next version of the Linux kernel may finally resolve the long-running problems associated with Linux on ARM processors. While devices like the Raspberry Pi have shown what can be done with Linux on the low-cost, low-power ARM processor, the burden of developing Linux on the growing number of ARM-derivative processors on the market has been, as Linus Torvalds himself has described it, "a fucking pain in the ass."

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Version 3.7 of the Linux kernel will be the first to support multiple versions of the ARM processor—a starting point toward a much-needed consolidation of Linux support for the system-on-a-chip architecture. In the long run, the changes could mean broader support for ARM by popular Linux distributions, making it easier for developers to build versions for a broader variety of target devices—everything from enterprise servers based on massive arrays of ARM processors to tablets and smartphones.

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Linux's fragmented support for the many variations of ARM processor architecture has been a source of frustration for Linux developers and users. Until now, each implementation of ARM by manufacturers has had its own associated kernel code tree, creating a code management nightmare.

According to a blog post by David Rusling, the chief technical officer of the Linaro nonprofit Linux-on-ARM coalition, "each new kernel release sees about 70,000 new lines of ARM code, whereas there's roughly 5,000 lines of new x86 code added."

All of that has made Torvalds very impatient in the past. Last year, in response to yet another code change request, he ranted, "Somebody in the ARM community really needs to step up and tell people to stop dicking around. I don't know who to 'blame.' I don't care. It really doesn't matter. I realize that ARM vendors do crazy shit and haven't figured out this whole 'platform' thing yet, but you guys need to push back on the people sending you crap."

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Kernel 3.7 will be the first step in getting a handle on ARM, unifying support for five different ARM architectures under a single kernel build:

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The Release:

Linux Kernel 3.7 Change Log on Kernel Newbies!

1.1. ARM multi-platform support
A typical linux distro for x86 PC computers can boot and work in hundreds of different PC (different CPU vendor, different GPU models, different motherboards and chipsets, etc) using a single distro install media. This ability to be able to boot in different hardware configurations is taken as a given in the PC world. However, it didn't exist in the Linux ARM world. The ARM ecosystem has historically been driven by the embedded world, where hardware enumeration isn't even possible in many cases, so each ARM kernel image was targetted for a specific embedded hardware target. It couldn't boot in other ARM systems.

In this release, the Linux ARM implementation has added "multi-plataform" support - the ability to build a single ARM kernel image that is able to boot multiple hardware. This will make much easier for distributors to support ARM plataforms.

Recommended LWN article: Supporting multi-platform ARM kernels


1.2. ARM 64 bit support
The newest ARM CPU model, ARM v8, adds 64 bit memory adressing capabilities for first time for the ARM world. The new 64 bit CPUs can run 32 bits code, but the 64 bit instruction set is completely new, not just 64 bit extensions to the 32 bit instruction set, so the Linux support has been implemented as a completely new architecture.

Recommended LWN article: Supporting 64-bit ARM systems


ArsTechnica Article!

Linux 3.7 released, bringing generic ARM support with it
by Andrew Cunningham - Dec 11 2012, 8:46pm EST

Linus Torvalds has officially announced that version 3.7 of the Linux kernel has gone stable, and that means good news for developers who work with ARM-based CPUs: among its other changes, Linux 3.7 is the first Linux kernel to include generic support for multiple ARM CPU architectures, reducing the amount of effort required to get Linux-based operating systems running on phones, tablets, and ARM-licensed developer boards like the Raspberry Pi.

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Tablet and smartphone users shouldn't get too excited just yet. As we originally reported, the current release's list of supported ARM architectures focuses overwhelmingly on server-oriented products—chips from Caldexa, Marvell, Altera, and Picohip are currently supported along with ARM's Versatile Express developer board, with support for more chips coming "in the next few releases" according to an October 2 post by Linus Torvalds. Additionally, it may yet be some time before this generic ARM support is worked into Android, which typically lags a few kernel versions behind. For Linux, though, this is the first step toward making ARM support more like x86 support—it may soon be possible to install operating systems on ARM-powered devices without the messy work of architecture-specific porting that is currently the norm.

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