* What is CONFIG_RTAS ? Which CPUs are concerned
@ 2019-01-28 18:20 Christophe Leroy
2019-01-28 18:32 ` Segher Boessenkool
0 siblings, 1 reply; 2+ messages in thread
From: Christophe Leroy @ 2019-01-28 18:20 UTC (permalink / raw)
To: Michael Ellerman, Benjamin Herrenschmidt, Paul Mackerras,
linuxppc-dev@ozlabs.org, Nicholas Piggin, Segher Boessenkool
Hello All,
I'm wondering what CONFIG_RTAS is. It makes use of one of the SPRN_SPRG,
ie SPRN_SPRG2.
What are the CPUs concerned by RTAS ? Is there any of the old CPUs which
have only 4 SPRGs (eg the 601), or could we use one in SPRG4-7 for it
and reuse SPRG2 for something else ?
The idea behind this question is to store physical address of PGDIR in
SPRG2 and then put virtual address of thread_struct instead of its
physical address in SPRG3, especially for when CONFIG_VMAP_STACK is set.
Thanks
Christophe
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: What is CONFIG_RTAS ? Which CPUs are concerned
2019-01-28 18:20 What is CONFIG_RTAS ? Which CPUs are concerned Christophe Leroy
@ 2019-01-28 18:32 ` Segher Boessenkool
0 siblings, 0 replies; 2+ messages in thread
From: Segher Boessenkool @ 2019-01-28 18:32 UTC (permalink / raw)
To: Christophe Leroy; +Cc: linuxppc-dev@ozlabs.org, Paul Mackerras, Nicholas Piggin
On Mon, Jan 28, 2019 at 07:20:43PM +0100, Christophe Leroy wrote:
> I'm wondering what CONFIG_RTAS is. It makes use of one of the SPRN_SPRG,
> ie SPRN_SPRG2.
>
> What are the CPUs concerned by RTAS ? Is there any of the old CPUs which
> have only 4 SPRGs (eg the 601), or could we use one in SPRG4-7 for it
> and reuse SPRG2 for something else ?
RTAS (run-time abstraction services) is as old as PowerPC itself. Yes there
is RTAS on various 6xx, and those do not have any SPRGs not defined in the
architecture.
RTAS is a feature of the firmware, or of the platform you could say. Not a
feature of CPUs.
Segher
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