Date: Fri, 16 Sep 2016 14:41:13 -0700 From: Mark Millard <markmi@dsl-only.net> To: FreeBSD PowerPC ML <freebsd-ppc@freebsd.org>, jau789@gmail.com Subject: Re: [Bug 205458] 11.0-CURRENT/10-STABLE powerpc64: a PowerMac G5 specific sys/powerpc/ofw/ofw_machdep.c change for reliable PowerMac G5 booting (with lots of RAM) Message-ID: <0F078304-8E8F-4EB1-B721-B6C4B885F118@dsl-only.net>
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Jukka A. Ukkonen jau789 at gmail.com wrote on Fri Sep 16 15:36:05 UTC =
2016 :
> it seems my PowerMac G5 is perfectly happy with this...
>=20
> __asm __volatile("mfsprg0 %0\n\t"
> : "=3D&r"(ofw_sprg0_save)
> :
> );
for the content in ofw_sprg_prepare(void).
Interestingly ofw_sprg0_save's use to save and restore requires that the =
same processor be in use in the restore side, ofw_sprg_restore(void): =
SPRG0 content is processor specific.
If the sprg0 save-restore is even required is not obvious to me: being =
required would imply that that something else is adjusting it between =
the save and restore code executions.
The following is just in the form of another simplest-local-changes =
experiment/analysis pass, not a "how it should be coded for general =
FreeBSD use" form for __powerpc64__ or at least for for =
PowerMac/iMac/Xserve G5's specifically. . .
Given what is reported above by Jukka it would appear that the above =
__asm lines possibly could be removed/disabled if ofw_sprg_restore(void) =
also had its __asm line removed/disabled: i.e.,
__asm __volatile("mtsprg0 %0" :: "r"(ofw_sprg0_save));
would no log be in use to access ofw_sprg0_save.
Effectively overall for the intended __powerpc64__ =
PowerMac(/iMac?/Xserver?) experimental context ofw_sprg_prepare and =
ofw_sprg_restore are then no-ops.
In effect ofw_sprg0_save and ofmsr[1] to ofmsr[4] would not be in =
significant use. But. . .
OF_initial_setup(void *fdt_ptr, void *junk, int (*openfirm)(void *))
still would have __asm references to ofmsr[1] through ofmsr[4] where =
they are initialized.
You might want to try deleting/disabling the __asm statements in =
ofw_sprg_prepare(void) and in ofw_sprg_restore(void) at the same time to =
see if it makes any difference. If it does make a difference that would =
be interesting and important. Otherwise it helps identify some more =
(PowerMac/. . . context specific) unnecessary code.
=3D=3D=3D
Mark Millard
markmi at dsl-only.net
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