[Libre-soc-dev] setvl lost its reserved fields (was: setvl gaining CTR mode)

[Jacob Lifshay]

On Sun, Jul 3, 2022, 01:50 lkcl <luke.leighton at gmail.com> wrote:

> second time of repeating. you ignored it once already.
>
> i'm not doing full redesigns of setvl at this late stage.
>

it's far from a full redesign if all you're doing is changing SVi's msb
(which is always 0) to be the fut_mode field rather than part of the SVi
field, and adding docs explaining what fut_mode is and how you currently
have to trap if it isn't zero.

nothing else changes: assembly syntax doesn't change, setvl's
implementation doesn't need to change, the decoder needs to check that that
bit is zero either way (if it doesn't it's incorrect or needs to trap some
other way), so that doesn't change either.

i expect that the whole change including all tests would take at most few
hours work since nearly everything is unmodified.

Also, this is effectively changing back to the design we already agreed on
iirc (see link below), that had been lost presumably when setvl was crammed
into the bitmanip major op.

https://bugs.libre-soc.org/show_bug.cgi?id=535

Jacob