linux-kernel - Re: [PATCH 2/2] powernv: Pass PSSCR value and mask to power9_idle

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Date:   Thu, 13 Oct 2016 16:53:57 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Stewart Smith <stewart@...ux.vnet.ibm.com>
Cc:     Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "skiboot@...ts.ozlabs.org" <skiboot@...ts.ozlabs.org>,
        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>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/2] powernv: Pass PSSCR value and mask to
 power9_idle_stop

Hi Stewart,

On Wed, Oct 12, 2016 at 04:35:35PM +1100, Stewart Smith wrote:
> 
> What if we just treat the 0xF state from firmware as special and set it
> to DEFAULT_PSSCR_MASK in that case? That deals with old skiboot, new
> kernel, and sets a pretty small special case that's easy to track into
> the future as something we should watch out for.

Yes, that will work. I will use this approach in the next version.

> 
> Additionally, if we make skiboot set sane values in ~DEFAULT_PSSCR_MASK
> for valid fields in PSSCR on boot/(also kexec?), then
> we should end up in a situation where everything works with everything
> (even if you don't get the best power saving). Specifically, new
> skiboot, old kernel... but it looks like there's nothing currently
> missing there

No we're not missing much there. From the code of the old kernel, I
see that if we pass the psscr_val instead of just the RL to
power9_idle_stop(), we end up saving all the SPRs in
power_enter_stop() even if the psscr_val didn't correspond to a deep
idle state.

But that should be ok.

> 
> Should this patch also have Fixes: 3005c597ba4 and CC to stable?

Yes, thanks for pointing it out. I shall mark the next version to
stable.

> 
> -- 
> Stewart Smith
> OPAL Architect, IBM.

--
Thanks and Regards
gautham.