linux-kernel - Re: [PATCH 4/4] PM / Domains: Propagate performance state updates

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Date:   Wed, 21 Nov 2018 11:12:43 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     ulf.hansson@...aro.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
        niklas.cassel@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] PM / Domains: Propagate performance state updates


On 11/21/2018 11:01 AM, Rajendra Nayak wrote:
> 
> 
> On 11/21/2018 10:46 AM, Viresh Kumar wrote:
>> On 21-11-18, 10:33, Rajendra Nayak wrote:
>>> Hi Viresh,
>>>
>>> On 11/5/2018 12:06 PM, Viresh Kumar wrote:
>>>> This commit updates genpd core to start propagating performance state
>>>> updates to master domains that have their set_performance_state()
>>>> callback set.
>>>>
>>>> A genpd handles two type of performance states now. The first one is the
>>>> performance state requirement put on the genpd by the devices and
>>>> sub-domains under it, which is already represented by
>>>> genpd->performance_state. The second type, introduced in this commit, is
>>>> the performance state requirement(s) put by the genpd on its master
>>>> domain(s). There is a separate value required for each master that the
>>>> genpd has and so a new field is added to the struct gpd_link
>>>> (link->performance_state), which represents the link between a genpd and
>>>> its master. The struct gpd_link also got another field
>>>> prev_performance_state, which is used by genpd core as a temporary
>>>> variable during transitions.
>>>>
>>>> We need to propagate setting performance state while powering-on a genpd
>>>> as well, as we ignore performance state requirements from sub-domains
>>>> which are powered-off. For this reason _genpd_power_on() also received
>>>> the additional parameter, depth, which is used for hierarchical locking
>>>> within genpd.
>>>>
>>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>>>> ---
>>>>    drivers/base/power/domain.c | 107 +++++++++++++++++++++++++++++-------
>>>>    include/linux/pm_domain.h   |   4 ++
>>>>    2 files changed, 92 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>>>> index 6d2e9b3406f1..81e02c5f753f 100644
>>>> --- a/drivers/base/power/domain.c
>>>> +++ b/drivers/base/power/domain.c
>>>> @@ -239,28 +239,86 @@ static void genpd_update_accounting(struct generic_pm_domain *genpd)
>>>>    static inline void genpd_update_accounting(struct generic_pm_domain *genpd) {}
>>>>    #endif
>>>> +static int _genpd_reeval_performance_state(struct generic_pm_domain *genpd,
>>>> +                       unsigned int state, int depth);
>>>> +
>>>>    static int _genpd_set_performance_state(struct generic_pm_domain *genpd,
>>>> -                    unsigned int state)
>>>> +                    unsigned int state, int depth)
>>>>    {
>>>> +    struct generic_pm_domain *master;
>>>> +    struct gpd_link *link;
>>>> +    unsigned int mstate;
>>>>        int ret;
>>>>        if (!genpd_status_on(genpd))
>>>>            goto out;
>>>
>>> This check here would mean we only propogate performance state
>>> to masters if the genpd is ON?
>>
>> Yeah, isn't that what should we do anyway? It is similar to clk-enable
>> etc. Why increase the reference count if the device isn't enabled and
>> isn't using the clock ?
> 
> I would think this is analogous to a driver calling clk_set_rate() first and
> then a clk_enable(), which is certainly valid.
> So my question is, if calling a dev_pm_genpd_set_performance_state()
> and then runtime enabling the device would work (and take care of propagating the performance
> state). In my testing I found it does not.

And the reason for that seems to be that we update the genpd status to GPD_STATE_ACTIVE
*after* we try to set the performance state, so we always hit this check which bails out
thinking the genpd is not ON.

> 
>>
>> Also you can see that I have updated the genpd power-on code to start
>> propagation to make sure we don't miss anything.
>>