[Arm-netbook] MNT Reform Campaign

[Paul Boddie]

On Tuesday 12. May 2020 19.20.37 Christopher Havel wrote:
> Forgive me for asking, because I didn't quite pass the requisite fervency
> test to be enrolled in the Joint OSHW-F|L|OSS Technical Militia ( :P ), but
> remind me, please, of a couple things, if I may ask them...?

I can try and provide some suggestions, but I'm sure Luke can give you plenty 
of additional insight.

> (1) Why are there none of these OSHW devices using existing x86-compatible
> CPUs/SoCs?

I can think of a few reasons, some mundane and some more important for open 
source hardware.

One mundane but practical reason might be that there is a degree of additional 
complexity in board design and assembly with x86(-64) products. Looking at 
recent AMD products where the socket support has been fairly stable, the 
actual CPUs seem to have large numbers of pins. If the CPUs are actually 
socketed, maybe the techniques involved are less demanding than having to 
mount the CPUs directly on the boards, but then I can still imagine that the 
engineering isn't going to be easy.

For lower-power products, things like the embedded Ryzen stuff uses a 
different socket type (FP5) to normal Ryzen (AM4) - even the GE variants of 
normal Ryzen - and for some products I get the impression that the "socket" is 
just an indicator of the footprint and not an actual socket where you would be 
able to swap out the CPUs, but I could be wrong. And this is just AMD: Intel 
seem to change "socket" types all the time which would make everything more 
complicated and demanding. It isn't a surprise that there are just a handful 
of major mainboard vendors presumably having deep relationships to AMD and 
Intel.

For open source hardware, it is also potentially interesting to make low-power 
products, and here the power consumption of x86(-64) seems rather high. At the 
lower end, Intel seem to offer Atom-branded and Pentium-branded products that 
consume a few watts and seem to be based on relatively modern 
microarchitectures, and they did try to make embedded CPUs based on earlier 
microarchitectures - Quark, I think it was - that didn't catch on.

There is also a strong temptation to drop the x86 legacy altogether when you 
are not strongly invested in it. My impression is that SoCs for other 
architectures provide a degree of freedom from that legacy at the cost of a 
lack of standardisation. But it also means that there is a certain potential 
to avoid the more recent undesirable aspects of BIOS-related technologies, 
although there are x86-64-based laptops being sold that supposedly address 
such issues (in certain regards) and that are promoted as being friendly to 
Free Software even if they are not actually open source hardware as well.

> (2a) Are there any meaningful barriers to creating an OSHW-compatible x86
> CPU/SoC, independent of major chip houses (Intel, AMD) or established niche
> players (VIA, etc)?

Yes: patents. VIA only got away with releasing x86-compatible products because 
of some ancient agreement, as far as I remember, and Intel has been rather 
aggressive in preventing new entrants getting into the market. The histories 
of various companies passing through the x86 market are quite interesting: 
Cyrix, NexGen, National Semiconductor, IBM, Transmeta, and so on. Many of the 
alternative x86 implementations seem to have ended up at AMD over the years.

> (2b) I've heard noises of a homegrown sort of effort out of China, from a
> company and fab house over there... could that CPU be considered as an
> acceptable candidate for such an effirt, and if not, why...? (I assume not,
> and because "China!", but I'm wide open here.)

I think I heard something of the sort, too. There is nothing to stop anyone 
from making their own x86(-64) implementation technically, and we must be at 
the stage where a fair amount of the x86 architecture is not patent 
encumbered. Then again, there are plenty of other architectures that are a lot 
more interesting and performant than old-style x86.

That brings us to another pertinent point about modern x86-64 CPUs: the 
performance presumably comes from the microarchitecture that is effectively 
internal and specific to each of the big players' products (things like Core 
and Zen). Seeking to compete with existing x86 products would involve a 
colossal amount of work replicating what they have managed to do with those 
microarchitecture efforts.

Well, those were just a few ideas, some more credible than others.

Paul