linux-kernel - Re: [PATCH v2 19/48] opp: Fix adding OPP entries in a wrong order if rate is unavailable

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Message-ID: <20201224062826.frppxddfinjomfui@vireshk-i7>
Date:   Thu, 24 Dec 2020 11:58:27 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 19/48] opp: Fix adding OPP entries in a wrong order if
 rate is unavailable

On 23-12-20, 23:36, Dmitry Osipenko wrote:
> 23.12.2020 07:34, Viresh Kumar пишет:
> > On 22-12-20, 22:19, Dmitry Osipenko wrote:
> >> 22.12.2020 12:12, Viresh Kumar пишет:
> >>> rate will be 0 for both the OPPs here if rate_not_available is true and so this
> >>> change shouldn't be required.
> >>
> >> The rate_not_available is negated in the condition. This change is
> >> required because both rates are 0 and then we should proceed to the
> >> levels comparison.
> > 
> > Won't that happen without this patch ?
> 
> No

This is how the code looks like currently:

int _opp_compare_key(struct dev_pm_opp *opp1, struct dev_pm_opp *opp2)
{
	if (opp1->rate != opp2->rate)
		return opp1->rate < opp2->rate ? -1 : 1;
	if (opp1->bandwidth && opp2->bandwidth &&
	    opp1->bandwidth[0].peak != opp2->bandwidth[0].peak)
		return opp1->bandwidth[0].peak < opp2->bandwidth[0].peak ? -1 : 1;
	if (opp1->level != opp2->level)
		return opp1->level < opp2->level ? -1 : 1;
	return 0;
}

Lets consider the case you are focussing on, where rate is 0 for both the OPPs,
bandwidth isn't there and we want to run the level comparison here.

Since both the rates are 0, (opp1->rate != opp2->rate) will fail and so we will
move to bandwidth check which will fail too. And so we will get to the level
comparison.

What am I missing here ? I am sure there is something for sure as you won't have
missed this..

-- 
viresh