linux-kernel - Re: [RFC v2 01/11] OPP: Don't overwrite rounded clk rate

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Date:   Mon, 17 Jun 2019 09:37:02 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>, swboyd@...omium.org,
        vincent.guittot@...aro.org, mturquette@...libre.com
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-spi@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-scsi@...r.kernel.org, ulf.hansson@...aro.org,
        dianders@...omium.org, rafael@...nel.org
Subject: Re: [RFC v2 01/11] OPP: Don't overwrite rounded clk rate



On 6/17/2019 9:20 AM, Viresh Kumar wrote:
> On 14-06-19, 10:57, Viresh Kumar wrote:
>> Hmm, so this patch won't break anything and I am inclined to apply it again :)
>>
>> Does anyone see any other issues with it, which I might be missing ?
> 
> I have updated the commit log a bit more to clarify on things, please let me
> know if it looks okay.
> 
>      opp: Don't overwrite rounded clk rate
>      
>      The OPP table normally contains 'fmax' values corresponding to the
>      voltage or performance levels of each OPP, but we don't necessarily want
>      all the devices to run at fmax all the time. Running at fmax makes sense
>      for devices like CPU/GPU, which have a finite amount of work to do and
>      since a specific amount of energy is consumed at an OPP, its better to
>      run at the highest possible frequency for that voltage value.
>      
>      On the other hand, we have IO devices which need to run at specific
>      frequencies only for their proper functioning, instead of maximum
>      possible frequency.
>      
>      The OPP core currently roundup to the next possible OPP for a frequency
>      and select the fmax value. To support the IO devices by the OPP core,
>      lets do the roundup to fetch the voltage or performance state values,
>      but not use the OPP frequency value. Rather use the value returned by
>      clk_round_rate().
>      
>      The current user, cpufreq, of dev_pm_opp_set_rate() already does the
>      rounding to the next OPP before calling this routine and it won't
>      have any side affects because of this change.

Looks good to me. Should this also be documented someplace that dev_pm_opp_set_rate()
would not be able to distinguish between its users trying to scale CPU/GPU's vs IO
devices, so its the callers responsibility to round it accordingly before calling the
API?

>      
>      Signed-off-by: Stephen Boyd <swboyd@...omium.org>
>      Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
>      [ Viresh: Massaged changelog and use temp_opp variable instead ]
>      Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> 
> 

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