Re: [RFC 0/3] Integrate Support for self-save and determine

[Pratik Sampat]

Thanks for your comments Ram,
> > A list of preferred SPRs are maintained in the kernel which contains two
> > properties:
> > 1. supported_mode: Helps in identifying if it strictly supports self
> >                     save or restore or both.
> Will be good to capture the information that, 'supported_mode' gets
> initialized using the information from the device tree.
>
> > 2. preferred_mode: Calls out what mode is preferred for each SPR. It
> >                     could be strictly self save or restore, or it can also
> >                     determine the preference of  mode over the other if both
> >                     are present by encapsulating the other in bitmask from
> >                     LSB to MSB.
> and 'preferred_mode'  is statically initialized.
Sure thing, I'll mention that.

> > Below is a table to show the Scenario::Consequence when the self save and
> > self restore modes are available or disabled in different combinations as
> > perceived from the device tree thus giving complete backwards compatibly
> > regardless of an older firmware running a newer kernel or vise-versa.
> >
> > SR = Self restore; SS = Self save
> >
> > .-----------------------------------.----------------------------------------.
> > |             Scenario              |                Consequence             |
> > :-----------------------------------+----------------------------------------:
> > | Legacy Firmware. No SS or SR node | Self restore is called for all         |
> > |                                   | supported SPRs                         |
> > :-----------------------------------+----------------------------------------:
> > | SR: !active SS: !active           | Deep stop states disabled              |
> > :-----------------------------------+----------------------------------------:
> > | SR: active SS: !active            | Self restore is called for all         |
> > |                                   | supported SPRs                         |
> > :-----------------------------------+----------------------------------------:
> > | SR: active SS: active             | Goes through the preferences for each  |
> > |                                   | SPR and executes of the modes          |
> > |                                   | accordingly. Currently, Self restore is|
> > |                                   | called for all the SPRs except PSSCR   |
> > |                                   | which is self saved                    |
> > :-----------------------------------+----------------------------------------:
> > | SR: active(only HID0) SS: active  | Self save called for all supported     |
> > |                                   | registers expect HID0 (as HID0 cannot  |
> > |                                   | be self saved currently)               |
> Not clear, how this will be conveyed to the hypervisor? Through the
> device tree or through some other means?
This information will be conveyed through the device tree. I'll frame a sentence
that makes this more explicit.

> > :-----------------------------------+----------------------------------------:
> > | SR: !active SS: active            | currently will disable deep states as  |
> > |                                   | HID0 is needed to be self restored and |
> > |                                   | cannot be self saved                   |
> > '-----------------------------------'----------------------------------------'
> >
> > Pratik Rajesh Sampat (3):
> >    powerpc/powernv: Interface to define support and preference for a SPR
> >    powerpc/powernv: Introduce Self save support
> >    powerpc/powernv: Parse device tree, population of SPR support
> >
> >   arch/powerpc/include/asm/opal-api.h        |   3 +-
> >   arch/powerpc/include/asm/opal.h            |   1 +
> >   arch/powerpc/platforms/powernv/idle.c      | 431 ++++++++++++++++++---
> >   arch/powerpc/platforms/powernv/opal-call.c |   1 +
> >   4 files changed, 379 insertions(+), 57 deletions(-)
> >
> > --
> > 2.21.0