[PATCH v5 0/5] powernv:stop: Use psscr_val,mask provided by firmware

[Gautham R. Shenoy]

From: "Gautham R. Shenoy" <ego@xxxxxxxxxxxxxxxxxx>

This is the fifth iteration of the patchset to use the psscr_val and
psscr_mask provided by the firmware for each of the stop states.

The previous versions can be found here:
[v4]: https://lkml.org/lkml/2016/12/9/288
[v3]: https://lkml.org/lkml/2016/11/10/37
[v2]: https://lkml.org/lkml/2016/10/27/143
[v1]: https://lkml.org/lkml/2016/9/29/45

This version addresses the feedback provided by Balbir and Vaidy to
v4. The key changes are:

- The current code had some functions/variables names containing
  arch300_* while others had power9*_. Uniformly rename this to arch300_*.

- Add a comment for POWERNV_THRESHOLD_LATENCY_NS.

- In case of a new firmware, validate that the PSSCR values provided
  by the firmware preserves the following invariants as required by the ISA:
    a) While running in Hypervisor mode (HV=1), EC bit must have the
    same value as ESL bit.
    b) For deep stop states that result in state-loss, ESL bit must be set.

- Optimize the sequence of instructions before executing stop with
  ESL=EC=0. Reduce one instruction.

- Fixed the typos in the Documentation for the device-tree bindings
  describing the stop-states exposed by the firmware.

Synopsis
==========
In the current implementation, the code for ISA
v3.0 stop implementation has a couple of shortcomings.

a) The code hand-codes the values for ESL,EC,TR,MTL bits of PSSCR and
   uses only the RL field from the firmware. While this is not
   incorrect, since the hand-coded values are legitimate, it is not a
   very flexible design since the firmware has the capability to
   communicate these values via the "ibm,cpu-idle-state-psscr" and
   "ibm,cpu-idle-state-psscr-mask" properties. In case where the
   firmware provides values for these fields that is different from
   the hand-coded values, the current code will not work as intended.

b) Due to issue a), the current code assumes that ESL=EC=1 for all the
   stop states and hence the wakeup from the stop instruction will
   happen at 0x100, the system-reset vector. However, the ISA v3.0
   allows the ESL=EC=0 behaviour where the corresponding stop-state
   loses no state and wakes up from the subsequent instruction. The
   current code doesn't handle this case.
   
This patch series addresses these issues.

The first patch in the series renames the existing
IDLE_STATE_ENTER_SEQ macro to IDLE_STATE_ENTER_SEQ_NORET. It reuses
the name IDLE_STATE_ENTER_SEQ for entering into stop-states which wake
up at the subsequent instruction.

The second patch in the series uniformly renames all occurences of "power9"
to "arch300" thereby making the variable/function names consistent.

The third patch adds a helper function in cpuidle-powernv.c for
initializing entries of the powernv_states[] table that is passed to
the cpu-idle core. This eliminates some of the code duplication in the
function that discovers and initializes the stop states.

The fourth patch in the series fixes issues a) and b) by ensuring that
the psscr-value and the psscr-mask provided by the firmware are what
will be used to set a particular stop state. It also adds support for
handling wake-up from stop states which were entered with ESL=EC=0.
It validates hat the psscr values exposed by the firmware maintains
the invariants mentioned in the ISA.

The fourth patch also handles the older firmware which sets only the
Requested Level (RL) field in the psscr and psscr-mask exposed in the
device tree. In the presence of such older firmware, this patch will
set the default sane values for for remaining PSSCR fields (i.e PSLL,
MTL, ESL, EC, and TR).

The fifth patch provides the documentation for the device-tree
bindings describing the idle state properties under the @power-mgt
node in the device-tree.

The skiboot patch populates all the relevant fields in the PSSCR
values and the mask for all the stop states can be found here:
https://lists.ozlabs.org/pipermail/skiboot/2016-September/004869.html

Gautham R. Shenoy (5):
  powernv:idle: Add IDLE_STATE_ENTER_SEQ_NORET macro
  powernv:stop: Uniformly rename power9 to arch300
  cpuidle:powernv: Add helper function to populate powernv idle states.
  powernv: Pass PSSCR value and mask to power9_idle_stop
  Documentation:powerpc: Add device-tree bindings for power-mgt

 .../devicetree/bindings/powerpc/opal/power-mgt.txt | 125 ++++++++++++++++++
 arch/powerpc/include/asm/cpuidle.h                 |  49 ++++++-
 arch/powerpc/include/asm/processor.h               |   3 +-
 arch/powerpc/kernel/exceptions-64s.S               |   6 +-
 arch/powerpc/kernel/idle_book3s.S                  |  53 ++++----
 arch/powerpc/platforms/powernv/idle.c              | 142 ++++++++++++++++++---
 arch/powerpc/platforms/powernv/powernv.h           |   3 +-
 arch/powerpc/platforms/powernv/smp.c               |  14 +-
 drivers/cpuidle/cpuidle-powernv.c                  | 129 +++++++++++++------
 include/linux/cpuidle.h                            |   1 +
 10 files changed, 435 insertions(+), 90 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

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1.9.4