linux-kernel - Re: [PATCH v10 2/6] PM / Domains: core changes for multiple states

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Date:	Tue, 10 Nov 2015 12:02:28 +0100
From:	Axel Haslam <ahaslam@...libre.com>
To:	Zhaoyang Huang <zhaoyang.huang@...aro.org>
CC:	Kevin Hilman <khilman@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Lina Iyer <lina.iyer@...aro.org>, geert@...der.be,
	k.kozlowski.k@...il.com, rjw@...ysocki.net,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	bcousson@...libre.com, mturquette@...libre.com,
	Axel Haslam <ahaslam+renesas@...libre.com>
Subject: Re: [PATCH v10 2/6] PM / Domains: core changes for multiple states

Hi Zhaoyang,

>     @@ -576,6 +584,8 @@ static void pm_genpd_sync_poweroff(struct
>     generic_pm_domain *genpd,
>                  || atomic_read(&genpd->sd_count) > 0)
>                      return;
>
>     +       /* Choose the deepest state when suspending */
>     +       genpd->state_idx = genpd->state_count - 1;
>
> if there is no governor configured, does it mean that we just try the
> deepest one here?
>

If a governor is not configured, there is no way to choose between the 
states, and the state_idx will not change. so it will remain the one set 
at the genpd init function wich is the same as here: the deepest state. 
(state_count -1). In other words, if there is no governor, there
is only one state: the deepest.

About setting the deepest state in this particular place, My 
understanding is that this code will be called in suspend path,
and in this case genpd_poweroff is not called, hence the genpd governor 
is not called either. Because there are many other things happening 
during suspend/resume, i think that suspend/resume is a slow procedure 
that will most likely not honor the device qos constraints, so i set the 
genpd to its deepest state.

Regards
Axel
>              genpd_power_off(genpd, timed);
>
>              genpd->status = GPD_STATE_POWER_OFF;
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