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Re: [2/2 ABI and toolchain part] Support Raspberry Pi [0-3] in big-endian mode

On 2020/11/24 23:59, Jason Thorpe wrote:

On Nov 24, 2020, at 4:28 AM, Rin Okuyama <> wrote:

CPU_CONTROL_SWP_ENABLE bit is missing for ARMv6. See cp15 c1 register
bit definition on p.3-46 of ARM1176JZF-S Technical Reference Manual:

| [10] F bit - Should Be Zero

Also, it does not work for MULTIPROCESSOR in principle:


Oops, it was wrong. ARM ARM "ARMv7-A and ARMv7-R edition", or, more
concisely, their web page says swp{,b} instructions on ARMv7 work for
MP system:

| Limitations of SWP and SWPB
| ...
| In a multi-core system, preventing access to main memory for all
| processors for the duration of a swap instruction can reduce
| overall system performance.
| ...

So, I guess that mrg@ disabled swp{,b} for MULTIPROCESSOR not because
instructions their-selves do not work, but because there are other
problems for ARMv5 userland on MP environment. As Robert suggested in
his previous message, multi-threaded applications for ARMv5 do not
work on MP system. See port-arm/55704 by myself:

Matthew, is this reason why you disabled them for MP kernel?


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