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ARM Is a Promising Platform But Needs To Learn From the PC
jbrodkin writes "Linux and ARM developers have clashed over what's been described as a 'United Nations-level complexity of the forks in the ARM section of the Linux kernel.' Linus Torvalds addressed the issue at LinuxCon this week on the 20th anniversary of Linux, saying the ARM platform has a lot to learn from the PC. While Torvalds noted that 'a lot of people love to hate the PC,' the fact that Intel, AMD, and hardware makers worked on building a common infrastructure 'made it very efficient and easy to support.' ARM, on the other hand, 'is missing it completely,' Torvalds said. 'ARM is this hodgepodge of five or six major companies and tens of minor companies making random pieces of hardware, and it looks like they're taking hardware and throwing it at a wall and seeing where it sticks, and making a chip out of what's stuck on the wall.'"
All of which is, more or less, interchangeable. The Intel x86/IBM PC platform, despite its many flaws, has reached a stable point where there are well accepted and commonly implemented standards for the boot process, the storage formats, the hardware interfaces, etc. ARM, despite a "purer" and "simpler" instruction architecture, lacks much of this common surrounding infrastructure.
What is a desktop in the PC world is your SOC in the embedded world. It even comes with RAM and Flash (not on chip, but on package), if you want to.
The difference is that the PC environment has over a long time filtered down to a few typical devices for each type. Your network hardware is probably Realtek, or maybe Intel or an embedded AMD chip. You graphics card is NVidia, AMD or Intel. Your mouse does not matter, because it always talk USB HID etc.
In the ARM world, you also have standard components, but every integrator makes tiny (and usually pointless) changes that render them incompatible on the software level. Linus is right - this is neither necessary nor sustainable. It is one of the reasons that you can get software updates for a 5 year old PC, but not for a 6 months old smartphone.
They're not trying to cut corners for the hell of it, but for performance, power usage, and other actual engineering reasons.
You just cant build smartphones and tablets with that same common architecture, or else you're adding too many chips and circuits you don't need.
It's no big deal that PC's ship with empty PCI slots and huge chunks of the bios and chipset that are never used but rarely. (Onboard raid, ECC codes, so on and so on), but when you're trying to put together a device as trim and minimalist as possible, you're going to end up with something slightly different for each use case.
I'm pretty certain he'd prefer a consortium that produces a common set of standards, but he raises an important point.
Choice costs.
It's wonderful that you have the a massively wide variety of choices, unconstrained by the a central authority, but don't forget that the cost of having that choice is going to be significant. There's a reason that almost all lines of business tend towards either a few big winners or, if the product is essentially identical, commoditization.
It's why I often wonder at why Linux users dream about taking over the desktop. If that did occur, it would mean a drive to lower cost that would result, almost inevitably, in the wholesale adoption of s single choice, reducing all the other choices to total irrelevance.
Is Linus Torvalds (implicitly, at least) criticizing ARM because it is open and therefore anyone can create their own version of it? As opposed to x86, which has a restricted licensing set (AMD/Intel/Via... Via still exists, right?)? Because that is, AFAICT, exactly why ARM is so varied: anyone can roll their own. With the result that many do.
ARM is not any more "open" than x86. To sell chips implementing modern versions of either instruction set, you must obtain a license from at least one company and nothing prevents you from extending that instruction set. Many companies have implemented (and often extened) each set over the years, though there are fewer implementing x86 now than ARM. There are probably fewer implementors of x86 because it is much more complex.
I think Linus is criticizing the lack of a common platform surrounding ARM rather than the instructions themselves. The instruction set of x86 chips has grown a lot, especially with x86_64, but the way you boot a PC hasn't changed much for example.
It is NOTHING like computers in the 70s and 80s.
In the 80s, you had machines made out of standard 3rd party components. Your CPU was the same as the next guy even if he got his computer from a competing brand. This is why an Atari could emulate a Mac. The actual CPU was a particular part that everyone bought from the same place. This is why you can have versions of Linux targeting those 80s/90s era machines. A 68000 in one machine is the same as the next, or a 6502, or a 68030.
The old home computer landscape seems positively orderly by comparison.
A Pirate and a Puritan look the same on a balance sheet.
The CPUs were standard, but little else was. Sure, the C-64 and Atari 800 both had a 6502-based CPU, but they also had different video chips, different sound chips, different and mutually incompatible disk drive formats and serial communications protocols, etc. One nice thing was that even though each company used their proprietary chips, they didn't feel the need to hide implementation details from users. If you wanted to know exactly what each register in the VIC-II chip did, it was right there in the manual.