Hi!

I was checking for dpkg arch definitions to cleanup and stumbled over
the uclinux-any ones (added as part of #455501), where I noticed the
µCLinux fork got merged into mainline Linux in 2.5.46, and then
several of the no-MMU ports got removed from there more recently.

Is this still being used at all as uclinux instead of just linux with
no mmu? If it is, then I see no problem with keeping these at all,
these definitions just looked somewhat dead at this point.

Thanks,
Guillem

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Hi!

On Mon, 2023-11-13 at 21:41:48 +0900, Simon Richter wrote:

On 13.11.23 19:08, Guillem Jover wrote:

I was checking for dpkg arch definitions to cleanup and stumbled over
the uclinux-any ones (added as part of #455501), where I noticed the µCLinux fork got merged into mainline Linux in 2.5.46, and then
several of the no-MMU ports got removed from there more recently.

I must admit that I haven't really used uClinux, or rather any MMUless architecture in ages, and the company that I originally wrote this for (and which did indeed run an internal Debian mirror with packages for a
big-endian MMUless ARM box running uClinux) has since shut down, so I
believe there are no users left.

I'm not sure if it's entirely dead or just about to get a resurgence because of FPGAs and FPGA SoCs with integrated hard CPUs that are gaining in popularity.

On the pure FPGA side, my expectation is that if it runs Linux, it will have an MMU.

The major commercial soft CPUs, Microblaze and NiosII, have MMU designs with very little overhead (basically, a TLB and a processor mode for the TLB miss handler to run in), so there is little incentive to run MMUless.

RISC-V, ARM and SPARC implementations for FPGAs might be interesting to run MMUless (because their MMU interface standards take a lot of resources to implement), but I'm not aware of anyone actually doing that.

On the SoC side, I think most available ICs contain an MMU, and those that don't aren't really used with Linux (there are some MMUless Cortex-R cores that can address enough memory, but I doubt that's a practical concern).

So I think these can be removed.

Thanks for the background info! I'll then queue the patch removing
these.

Regards,
Guillem

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