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

From: Pratik Sampat
Date: Mon Jan 06 2020 - 04:45:41 EST

Thanks for your comments Ram,
A list of preferred SPRs are maintained in the kernel which contains two
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
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(-)