linux-kernel - Re: [PATCH v2 1/6] soc: qcom: rpmpd: Add a powerdomain driver to model corners

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Date:   Thu, 31 May 2018 09:23:53 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     David Collins <collinsd@...eaurora.org>,
        Ulf Hansson <ulf.hansson@...aro.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 v2 1/6] soc: qcom: rpmpd: Add a powerdomain driver to
 model corners

Hi David,

On 05/30/2018 11:57 PM, David Collins wrote:
> Hello Rajendra,
> 
> On 05/30/2018 03:14 AM, Rajendra Nayak wrote:
>> On 05/30/2018 02:47 PM, Ulf Hansson wrote:
>>> On 25 May 2018 at 12:01, Rajendra Nayak <rnayak@...eaurora.org> wrote:
> ...
>>>> +               pm_genpd_init(&rpmpds[i]->pd, NULL, true);
>>>
>>> Question: Is there no hierarchical topology of the PM domains. No
>>> genpd subdomains?
>>
>> The hierarchy if any is all handled by the remote core (RPM in this case).
>> For Linux its just a flat view.
> 
> There is one special case that we'll need to handle somehow.  The APPS
> vlvl request for VDD_MX needs to be greater than or equal to the vlvl
> request for VDD_CX.  Can you please add the necessary code to achieve
> this?  RPMh hardware doesn't handle this hardware requirement due to
> concerns about modem use case latency.

Sure, I'll take a look at it.

> 
> Please note that this is handled in a somewhat hacky manner [1] with the
> downstream rpmh-regulator driver by specifying VDD_MX as the parent of
> VDD_CX and VDD_MX_AO as the parent of VDD_CX_AO with a dropout voltage of
> -1.  That way, enabling CX causes MX to be enabled and voltage level
> requests are propagated from CX to MX (the -1 is ignored because it is
> rounded up within the sparse vlvl numbering space).

I can't see how else to handle this but with a fake parent/child relation,
which also means we might need support to propagate performance states for
power domains up the parents, which I think was initially supported but
later dropped since we thought this wasn't needed for now.
We might need to take a re-look at it to support this usecase.

thanks,
Rajendra

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