linux-kernel - Re: [PATCH v3 0/3] powernv:stop: Use psscr

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Date:   Tue, 29 Nov 2016 17:34:03 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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>,
        Oliver O'Halloran <oohall@...il.com>
Cc:     "\"linuxppc-dev"@lists.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, "skiboot\""@lists.ozlabs.org
Subject: Re: [PATCH v3 0/3] powernv:stop: Use psscr_val,mask provided by
 firmware



On 10/11/16 18:54, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> This is the third 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:
> 
> [v2]: https://lkml.org/lkml/2016/10/27/143
> [v1]: https://lkml.org/lkml/2016/9/29/45
> 
> This version fixes a couple of bugs pertaining to strncpy and
> initialization of the target-residency values of nap and sleep
> which were pointed out by Paul and Oliver in the earlier version.
> 
> 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.
>    

Sounds reasonable

Balbir Singh.