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Message-ID: <1b6bcd31-1dc8-abf7-304a-4de95b8f998b@gmail.com>
Date: Thu, 11 Oct 2018 12:55:49 -0700
From: Frank Rowand <frowand.list@...il.com>
To: Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Cc: huntbag@...ux.vnet.ibm.com, npiggin@...il.com,
benh@...nel.crashing.org, mpe@...erman.id.au,
ego@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH v2 0/3] New device-tree format and Opal based idle
save-restore
+ devicetree mail list
On 10/11/18 06:22, Akshay Adiga wrote:
> Previously if a older kernel runs on a newer firmware, it may enable
> all available states irrespective of its capability of handling it.
> New device tree format adds a compatible flag, so that only kernel
> which has the capability to handle the version of stop state will enable
> it.
>
> Older kernel will still see stop0 and stop0_lite in older format and we
> will depricate it after some time.
>
> 1) Idea is to bump up the version string in firmware if we find a bug or
> regression in stop states. A fix will be provided in linux which would
> now know about the bumped up version of stop states, where as kernel
> without fixes would ignore the states.
>
> 2) Slowly deprecate cpuidle/cpuhotplug threshold which is hard-coded
> into cpuidle-powernv driver. Instead use compatible strings to indicate
> if idle state is suitable for cpuidle and hotplug.
>
> New idle state device tree format :
> power-mgt {
> ...
> ibm,enabled-stop-levels = <0xec000000>;
> ibm,cpu-idle-state-psscr-mask = <0x0 0x3003ff 0x0 0x3003ff>;
> ibm,cpu-idle-state-latencies-ns = <0x3e8 0x7d0>;
> ibm,cpu-idle-state-psscr = <0x0 0x330 0x0 0x300330>;
> ibm,cpu-idle-state-flags = <0x100000 0x101000>;
> ibm,cpu-idle-state-residency-ns = <0x2710 0x4e20>;
> ibm,idle-states {
> stop4 {
> flags = <0x207000>;
> compatible = "ibm,state-v1",
> "opal-support";
> type = "cpuidle";
> psscr-mask = <0x0 0x3003ff>;
> handle = <0x102>;
> latency-ns = <0x186a0>;
> residency-ns = <0x989680>;
> psscr = <0x0 0x300374>;
> };
> ...
> stop11 {
> ...
> compatible = "ibm,state-v1",
> "opal-support";
> type = "cpuoffline";
> ...
> };
> };
>
> High-level parsing algorithm :
>
> Say Known version string = "ibm,state-v1"
>
> for each stop state node in device tree:
> if (compatible has known version string)
> kernel takes care of stop-transitions
> else if (compatible has "opal-support")
> OPAL takes care of stop-transitions
> else
> Skip All deeper states
>
> When a state does not have both version support and opal support,
> Its possible to exit from a shallower state. Hence skipping all
> deeper states.
>
> OPAL support for idle states
> ----------------------------
>
> With this patch series, all the states that loose hypervisor state
> will be handled through opal_call.
>
> Patch 3 adds support for Saving/restoring of SPRs and resync-timebase
> in OPAL. Also all the decision making such as identifying first thread
> in the core and taking locks before restoring, etc are implemented in
> OPAL.
>
> How does it work ?
> -------------------
>
> Consider a case that stop4 has a bug. We take the following steps to
> mitigate the problem.
>
> 1) Change compatible string for stop4 in OPAL to "ibm-state-v2" and
> remove "opal-supported". ship the new firmware.
> The kernel ignores stop4 and all deeper states. But we will still have
> shallower states. Prevents from completely disabling stop states.
>
> 2) Implement workaround in OPAL and add "opal-supported". Ship new firmware
> The kernel uses opal for stop-transtion , which has workaround implemented.
> We get stop4 and deeper states working without kernel changes and backports.
> (and considerably less time)
>
> 3) Implement workaround in kernel and add "ibm-state-v2" as known versions
> The kernel will now be able to handle stop4 and deeper states.
>
> Changes from v1 :
> - Code is rebased on Nick Piggin's v4 patch "powerpc/64s: reimplement book3s
> idle code in C"
> http://patchwork.ozlabs.org/patch/969596/
> - All the states that loses hypervisor states will be handled by OPAL
> - All the decision making such as identifying first thread in
> the core and taking locks before restoring in such cases have also been
> moved to OPAL
>
>
> Abhishek Goel (1):
> cpuidle/powernv: save-restore sprs in opal
>
> Akshay Adiga (2):
> cpuidle/powernv: Add support for states with ibm,cpuidle-state-v1
> powernv/cpuidle: Pass pointers instead of values to stop loop
>
> arch/powerpc/include/asm/cpuidle.h | 9 +
> arch/powerpc/include/asm/opal-api.h | 4 +-
> arch/powerpc/include/asm/opal.h | 3 +
> arch/powerpc/include/asm/processor.h | 8 +-
> arch/powerpc/kernel/idle_book3s.S | 6 +-
> arch/powerpc/platforms/powernv/idle.c | 247 ++++++++++++++----
> .../powerpc/platforms/powernv/opal-wrappers.S | 2 +
> drivers/cpuidle/cpuidle-powernv.c | 46 ++--
> 8 files changed, 251 insertions(+), 74 deletions(-)
>
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