Re: [PATCH 5/5] powernv:idle: Disable LOSE_FULL_CONTEXT states when stop-api fails.

On Fri, 7 Jul 2017 23:07:10 +0530
Gautham R Shenoy [off-list ref] wrote:

On Fri, Jul 07, 2017 at 01:29:16AM +1000, Nicholas Piggin wrote:

quoted

On Wed,  5 Jul 2017 22:08:16 +0530
"Gautham R. Shenoy" [off-list ref] wrote:
  

quoted

From: "Gautham R. Shenoy" <redacted>

Currently, we use the opal call opal_slw_set_reg() to inform the that
the Sleep-Winkle Engine (SLW) to restore the contents of some of the
Hypervisor state on wakeup from deep idle states that lose full
hypervisor context (characterized by the flag
OPAL_PM_LOSE_FULL_CONTEXT).

However, the current code has a bug in that if opal_slw_set_reg()
fails, we don't disable the use of these deep states (winkle on
POWER8, stop4 onwards on POWER9).

This patch fixes this bug by ensuring that if the the sleep winkle
engine is unable to restore the hypervisor states in
pnv_save_sprs_for_deep_states(), then we mark as invalid the states
which lose full context.

As a side-effect, since supported_cpuidle_states in
pnv_probe_idle_states() consists of flags of only the valid states,
this patch will ensure that no other subsystem in the kernel can use
the states which lose full context on stop-api failures.  

Looks good. Is there something minimal we can do for stable here?

Aside question, do we need to restore LPCR at all with the SLW engine?
It gets set up again when by the idle wakeup code.  

quoted

And does POWER9 really need MSR and PSSCR restored by SLW? (going a bit
off topic here, I'm just curious)  

MSR is needed to be restored so that we wakeup with the right
endianness and with the IR,DR disabled.

And POWER8 does not require this?

PSSCR is set to a value so that in case of a special wakeup for a
deep-stop, the SLW can program the core to go back to the stop level
provided by the PSSCR value via the stop-api.

It always restores to deepest stop? Is there any way to restore to the
achieved stop level? Maybe there is no usefulness for that.

Thanks,
Nick