[PATCH] riscv: add 'pause' hint-instruction

[Nelson Chu]

Hi Philipp,

On Thu, Jan 7, 2021 at 1:30 AM Philipp Tomsich <philipp.tomsich@vrull.eu> wrote:
>
> Add support for the 'pause' hint-instruction, as specified in the
> "Zihintpause" extension.  The 'pause' instruction is encoded as a
> special form of a memory 'fence' (which is available as part of the
> base instruction set): the chosen encoding does not mandate any
> particular memory ordering and therefore is a true hint.

We have decided to accept the frozen extensions recently, if they are
almost unchanged and stable.  I have heard that the public review
period is finished for Zihintpause, and it is also frozen.  Therefore,
we should accept it, too.  As Kito suggested, I also agree that pause
instruction should be controlled by the zihintpause in the arch
string, so I add it into this patch, with the version v1.0.  But like
ZBA/ZBB/ZBC, none of the ISA specs define them yet, I have to define
them in the riscv_ext_version_table with the ISA_SPEC_CLASS_DRAFT.

Anyway, thanks for submitting this.  Already committed.

Nelson