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: <c5078503-ee14-0f84-85fd-9c6e55d2e897@gmail.com>
Date:   Mon, 9 Nov 2020 07:41:44 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "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>, 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()

09.11.2020 07:34, Viresh Kumar пишет:
> On 06-11-20, 16:18, Dmitry Osipenko wrote:
>> 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?
> 
> For that case you were always required to call
> dev_pm_opp_set_clkname(), otherwise how would the OPP core know which
> clock to set ? And the same shall work now as well.

Why _allocate_opp_table() grabs the first default clk of a device and
assigns it to the created table?