linux-kernel - Re: [PATCH 2/2] opp: Don't create an OPP table from dev_pm_opp_get_opp

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Message-ID: <ec9839dd-5d2d-0d6b-6563-b14da4af1a57@gmail.com>
Date:   Fri, 6 Nov 2020 16:18:19 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] opp: Don't create an OPP table from
 dev_pm_opp_get_opp_table()

06.11.2020 09:24, Viresh Kumar пишет:
> It has been found that some users (like cpufreq-dt and others on LKML)
> have abused the helper dev_pm_opp_get_opp_table() to create the OPP
> table instead of just finding it, which is the wrong thing to do. This
> routine was meant for OPP core's internal working and exposed the whole
> functionality by mistake.
> 
> Change the scope of dev_pm_opp_get_opp_table() to only finding the
> table. The internal helpers _opp_get_opp_table*() are thus renamed to
> _add_opp_table*(), dev_pm_opp_get_opp_table_indexed() is removed (as we
> don't need the index field for finding the OPP table) and so the only
> user, genpd, is updated.
> 
> Note that the prototype of _add_opp_table() was already left in opp.h by
> mistake when it was removed earlier and so we weren't required to add it
> now.

Hello Viresh,

It looks like this is not an entirely correct change because previously
it was possible to get an empty opp_table in order to use it for the
dev_pm_opp_set_rate(), which would fall back to clk_set_rate if table is
empty.

Now it's not possible to get an empty table and
dev_pm_opp_of_add_table() would error out if OPPs are missing in a
device-tree. Hence it's not possible to implement a fall back without
abusing opp_set_regulators() or opp_set_supported_hw() for getting the
empty table. Or am I missing something?