Re: gem driver for sun4m

On Saturday, July 18, 2026 10:19:40=E2=80=AFAM Eastern Daylight Time Jason =
Thorpe=20
wrote:
> > On Jul 18, 2026, at 2:56=E2=80=AFAM, Julian Coleman <[email protected]> =
wrote:
> >=20
> > When I added the SBus GEM support, I also couldn't find any documentati=
on
> >=20
> > for the best values - the only information I have is the:
> >  Specification for Sbus GEM Gigabit Ethernet ASIC (100-5544-03)
>=20
> I have a copy of "Specification for Sbus GEM Gigabit Ethernet ASIC
> (100-5544-03)=E2=80=9D.  The table that describes the SBus configuration =
register
> is on page 70, section 3.1.2.2, Table 3-2.

That was the document I was trying to track down, actually; it was mentione=
d=20
in the comments of if_gem_sbus.c, but the sun.com link was long dead. Altho=
ugh=20
just now I did some further searching for that exact title and managed to=20
track down a copy on archive.org: https://ia601700.us.archive.org/7/items/
SPARCDocs/gem_sbus-1.pdf

> [2:0] System Maximum Burst Support -- Tells if the host system supports 4=
,=20
8, or 16 word maximum burst size
> [3] System Extended -- When set means system is in 64 bit extended SBus=20
mode; when not set means system is in 32 bit SBus mode
> ...
> [9] Parity Enable -- Parity enable, enables parity checking

By omitting the system extended bit, I suppose it's probably operating with=
=20
shorter words than on sun4u. I spent quite a while wondering why BSIZE64=20
seemed fine, when the sun4m documentation for SBus says the maximum is a 32=
=20
byte burst.

It's also possible parity checking could be enabled if the platform support=
s=20
it, rather than making that architecture dependent. I might have to look in=
to=20
that.

> Anyway, I=E2=80=99ve checked in the changes and have teed them up for inc=
lusion in
> NetBSD 11.1, as well.
>=20
> Thanks for submitting them, Erik!
>=20
> -- thorpej

My pleasure! This has been a weekend project for me for a few months off-an=
d-
on, I was just glad to get it into a stable state so it could see the light=
 of=20
day.

=2DErik