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Date:   Fri, 3 Aug 2018 00:05:47 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
To:     Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        mpe@ellerman.id.au, benh@kernel.crashing.org,
        ego@linux.vnet.ibm.com, huntbag@linux.vnet.ibm.com
Subject: Re: [RFC PATCH 3/3] cpuidle/powernv: Conditionally save-restore
 sprs using opal
Message-ID: <20180803000547.08a37175@roar.ozlabs.ibm.com>
In-Reply-To: <20180802045132.12432-4-akshay.adiga@linux.vnet.ibm.com>
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        <20180802045132.12432-4-akshay.adiga@linux.vnet.ibm.com>
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On Thu,  2 Aug 2018 10:21:32 +0530
Akshay Adiga <akshay.adiga@linux.vnet.ibm.com> wrote:

> From: Abhishek Goel <huntbag@linux.vnet.ibm.com>
> 
> If a state has "opal-supported" compat flag in device-tree, an opal call
> needs to be made during the entry and exit of the stop state. This patch
> passes a hint to the power9_idle_stop and power9_offline_stop.
> 
> This patch moves the saving and restoring of sprs for P9 cpuidle
> from kernel to opal. This patch still uses existing code to detect
> first thread in core.
> In an attempt to make the powernv idle code backward compatible,
> and to some extent forward compatible, add support for pre-stop entry
> and post-stop exit actions in OPAL. If a kernel knows about this
> opal call, then just a firmware supporting newer hardware is required,
> instead of waiting for kernel updates.

Still think we should make these do-everything calls. Including
executing nap/stop instructions, restoring timebase, possibly even
saving and restoring SLB (although a return code could be used to
tell the kernel to do that maybe if performance advantage is enough).

I haven't had a lot of time to go through it, I'm working on moving
~all of idle_book3s.S to C code, I'd like to do that before this
OPAL idle driver if possible.

A minor thing I just noticed, you don't have to allocate the opal
spr save space in Linux, just do it all in OPAL.

Thanks,
Nick