linux-kernel - Re: [PATCH v2 0/3] powernv:stop: Use psscr

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Date:   Tue, 01 Nov 2016 05:21:05 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        "Shreyas B. Prabhu" <shreyasbp@...il.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, skiboot@...ts.ozlabs.org
Subject: Re: [PATCH v2 0/3] powernv:stop: Use psscr_val,mask provided by firmware

On Thursday, October 27, 2016 02:05:04 PM Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> Hi,
> 
> This is the second iteration of the patchset to use the psscr_val and
> psscr_mask provided by the firmware for each of the stop states.
> 
> The previous version can be found here: 
> https://lkml.org/lkml/2016/9/29/45
> 
> The main changes in this version are:
> 
> 1) Add a helper function in powernv-cpuidle.c to help initialize the
>    powernv_states cpuidle table.
> 
> 2) Handle the older firmware which populates only the Requested Level
>    (RL) fields of the psscr and psscr_mask in the device tree. This
>    patchset ensures that in the presence of the older firmware, the
>    other fields of PSSCR are initalized to sane default values.
> 
> 
> 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 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 third 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.
> 
> The third 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 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
> 
> The patches are based on top of
> git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git fixes
> 
> Gautham R. Shenoy (3):
>   powernv:idle: Add IDLE_STATE_ENTER_SEQ_NORET macro
>   cpuidle:powernv: Add helper function to populate powernv idle states.
>   powernv: Pass PSSCR value and mask to power9_idle_stop

OK

I need someone to review this for me.

Thanks,
Rafael