linux-kernel - Re: [PATCH v3 6/7] soc: qcom: Add RPMh Power domain driver

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Date:   Fri, 15 Jun 2018 11:25:22 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     David Collins <collinsd@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Andy Gross <andy.gross@...aro.org>, devicetree@...r.kernel.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/7] soc: qcom: Add RPMh Power domain driver

David, Rajendra,

On 14 June 2018 at 20:17, David Collins <collinsd@...eaurora.org> wrote:
> Hello Rajendra,
>
> On 06/13/2018 11:54 PM, Rajendra Nayak wrote:
>> On 06/14/2018 06:02 AM, David Collins wrote:
>>> On 06/11/2018 09:40 PM, Rajendra Nayak wrote:
> ...
>>>> +static int rpmhpd_power_off(struct generic_pm_domain *domain)
>>>> +{
>>>> +   struct rpmhpd *pd = domain_to_rpmhpd(domain);
>>>> +   int ret = 0;
>>>> +
>>>> +   mutex_lock(&rpmhpd_lock);
>>>> +
>>>> +   if (pd->level[0] == 0)
>>>> +           ret = rpmhpd_aggregate_corner(pd, 0);
>>>
>>> I'm not sure that we want to have the 'pd->level[0] == 0' check,
>>> especially when considering aggregation with the peer pd.  I understand
>>> its intention to try to keep enable state and level setting orthogonal.
>>> However, as it stands now, the final request sent to hardware would differ
>>> depending upon the order of calls.  Consider the following example.
>>>
>>> Initial state:
>>> pd->level[0] == 0
>>> pd->corner = 5, pd->enabled = true, pd->active_only = false
>>> pd->peer->corner = 7, pd->peer->enabled = true, pd->peer->active_only = true
>>>
>>> Outstanding requests:
>>> RPMH_ACTIVE_ONLY_STATE = 7, RPMH_WAKE_ONLY_STATE = 7, RPMH_SLEEP_STATE = 5
>>>
>>> Case A:
>>>      1. set pd->corner = 6
>>>              --> new value request: RPMH_SLEEP_STATE = 6
>>>              --> duplicate value requests: RPMH_ACTIVE_ONLY_STATE = 7,
>>>                      RPMH_WAKE_ONLY_STATE = 7
>>>      2. power_off pd->peer
>>>              --> no requests
>>
>> I am not sure why there would be no requests, since we do end up aggregating
>> with pd->peer->corner = 0.
>> So the final state would be
>>
>> RPMH_ACTIVE_ONLY_STATE = max(6, 0) = 6
>> RPMH_WAKE_ONLY_STATE = 6
>> RPMH_SLEEP_STATE = max(6, 0) = 6
>
> Argh, my example was ruined by a one character typo.  I meant to have:
>
>         Initial state:
>         pd->level[0] != 0
>
>
>>>
>>>      Final state:
>>>      RPMH_ACTIVE_ONLY_STATE = 7
>>>      RPMH_WAKE_ONLY_STATE = 7
>>>      RPMH_SLEEP_STATE = 6
>>>
>>> Case B:
>>>      1. power_off pd->peer
>>>              --> no requests
>>
>> Here it would be again be aggregation based on pd->peer->corner = 0
>> so,
>> RPMH_ACTIVE_ONLY_STATE = max(5, 0) = 5
>> RPMH_WAKE_ONLY_STATE = 5
>> RPMH_SLEEP_STATE = max(5, 0) = 5
>>
>>>      2. set pd->corner = 6
>>>              --> new value requests: RPMH_ACTIVE_ONLY_STATE = 6,
>>>                     RPMH_WAKE_ONLY_STATE = 6, RPMH_SLEEP_STATE = 6
>>>
>>>      Final state:
>>>      RPMH_ACTIVE_ONLY_STATE = 6
>>>      RPMH_WAKE_ONLY_STATE = 6
>>>      RPMH_SLEEP_STATE = 6
>>
>> correct,
>> RPMH_ACTIVE_ONLY_STATE = max(6, 0) = 6
>> RPMH_WAKE_ONLY_STATE = 6
>> RPMH_SLEEP_STATE = max(6, 0) = 6
>>
>>>
>>> Without the check, Linux would vote for the lowest supported level when
>>> power_off is called.  This seems semantically reasonable given that the
>>> consumer is ok with the power domain going fully off and that would be the
>>> closest that we can get.
>>
>> So are you suggesting I replace
>>
>>>> +   if (pd->level[0] == 0)
>>>> +           ret = rpmhpd_aggregate_corner(pd, 0);
>>
>> with
>>
>>>> +   ret = rpmhpd_aggregate_corner(pd, pd->level[0]);
>
> Yes, this is the modification that I'm requesting.
>
>
>> I can see what you said above makes sense but if its
>>> Initial state:
>>> pd->level[0] != 0
>>
>> Was that what you meant?
>
> Yes.

Apologize for jumping into the discussion.

I have a couple of ideas, that may simplify/improve things related to the above.

1) Would it be easier if genpd calls ->set_performance_state(0) before
it is about to call the ->power_off() callback? Actually Viresh wanted
that from the start, but I thought it was useless.

2) When device are becoming runtime suspended, the ->runtime_suspend()
callback of genpd is invoked (genpd_runtime_suspend()). However, in
there we don't care to re-evaluate the votes on the performance level,
but instead rely on the corresponding driver for the device to drop
the vote. I think it would be a good idea of managing this internally
in genpd instead, thus, depending on if the aggregated vote can be
decreased we should call  ->set_performance_state(new-vote). Of
course, once the device get runtime resumed, the votes needs to be
restored for the device.

What do you think?

[...]

Kind regards
Uffe