linux-kernel - Re: [PATCH 05/11] PM / devfreq: governors: Return device frequency limits instead of user limits

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Message-ID: <20180529193236.GH168650@google.com>
Date:   Tue, 29 May 2018 12:32:36 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:     Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH 05/11] PM / devfreq: governors: Return device frequency
 limits instead of user limits

On Mon, May 28, 2018 at 02:04:44PM +0900, MyungJoo Ham wrote:
> >The performance, powersave and simpleondemand governors can return
> >df->min/max_freq, which are the user defined frequency limits.
> >update_devfreq() already takes care of adjusting the target frequency
> >with the user limits if necessary, therefore we can return
> >df->scaling_min/max_freq instead, which is the min/max frequency
> >supported by the device at a given time (depending on the
> >enabled/disabled OPPs)
> >
> >Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> >---
> > drivers/devfreq/governor_performance.c    | 2 +-
> > drivers/devfreq/governor_powersave.c      | 2 +-
> > drivers/devfreq/governor_simpleondemand.c | 6 +++---
> > 3 files changed, 5 insertions(+), 5 deletions(-)
> >
> 
> Actually, even scaling_max_freq and scaling_min_freq are
> covered centerally at devfreq.c:update_devfreq();
> 
> Wouldn't it be sufficient to return UINT_MAX for performance
> and return UINT_MIN (0) for powersave, if the purpose is to
> remove redundancy?
> 
> In the same sense, we may return UINT_MAX for freq-increasing
> case for simpleondemand as well, because they are filtered
> centrally anyway.
> 
> (This commit might be better merged to 4/11 in that case as well.)

I did this in the first variant of the patch (before sending it in a
series), but Chanwoo Choi objected:

https://patchwork.kernel.org/patch/10404893/

I also still think that returning a constant would be the cleanest
solution if we can agree on this. What do you think about
DEVFREQ_MIN/MAX_FREQ (0/UINT_MAX) to make things slightly clearer?