linux-kernel - Re: [PATCH 5/5] OPP: Remove custom OPP helper support

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Message-ID: <d2a8c329-4469-f68a-5b4b-789a93725ea4@collabora.com>
Date:   Tue, 28 Jun 2022 13:04:01 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     Keerthy <j-keerthy@...com>, Dave Gerlach <d-gerlach@...com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        linux-kernel@...r.kernel.org,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 5/5] OPP: Remove custom OPP helper support

On 6/27/22 10:19, Viresh Kumar wrote:
> On 27-06-22, 10:09, Dmitry Osipenko wrote:
>> Yes, I missed that multi-clock OPP patch, thanks.
>>
>> Seems _opp_compare_key() won't work properly for the multi-clocks since
>> Tegra doesn't have bandwidth nor level for the 3d OPPs. Why does it need
>> to check opp_table->clk_count == 1? Shouldn't it be opp_table->clk_count
>>> 0?
> 
> The problem is that when we have multiple clocks, we can't assume any
> of them as primary. Its the combination of the clock frequencies that
> make them unique. Otherwise, what will happen if we have same
> frequency of the first clock in two OPPs, but different frequency of
> the second clock.
> 
> Because of this, we won't also support multiple clocks in all freq
> finder APIs, like dev_pm_opp_find_freq_exact(). We can't do that from
> just one frequency.
> 
> Ideally, the drivers should now be calling dev_pm_opp_set_opp() to set
> the OPP now.
> 
> For your case, I think you can just add levels (like index) in the OPP
> table. So we can uniquely identify each OPP.
> 

What about to bump the "by-level" sorting priority, making it above the
"by-rate" sorting and then always use the first clock for the "by-rate"
sorting? Then the multi-clock will work for Tegra without breaking dtbs
and those for whom this sorting option won't be appropriate will have to
add levels to the DT.

-- 
Best regards,
Dmitry