Re: New pmap module for m68k

[Romain Dolbeau <romain%dolbeau.org@localhost>]

Le lun. 10 nov. 2025 à 15:02, Jason Thorpe <thorpej%me.com@localhost> a écrit :
> I keep forgetting about the UPA bits (partially because the Hibler pmap uses one of them as a software-defined bit, which we thankfully got away with for all these years).
> Yes, it would be possible to do that with UPA, but it would need special support in the pmap module (and any other place that has reason to consult a PTE value).

As far as I can tell, only U0 (bits 8 in the page descriptor, visible
to pin UPA0) is used by the NetBSD kernel (for PG_W), while the first
available UR bit from the '040 (bits 11, not outputed to external
hardware) is not used. If PG_W was moved from bit 8 to bit 11, the UPA
bits would be freed for the SMP-intended purpose of snooping (with
Motorola suggesting wiring SC0/1 to UPA0/1).

Cordially,

-- 
Romain Dolbeau