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

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