linux-kernel - Re: [TEGRA194_CPUFREQ Patch 2/3] cpufreq: Add Tegra194 cpufreq driver

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Date:   Wed, 4 Dec 2019 16:57:49 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     sumitg <sumitg@...dia.com>
Cc:     rjw@...ysocki.net, catalin.marinas@....com, will@...nel.org,
        thierry.reding@...il.com, jonathanh@...dia.com, talho@...dia.com,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bbasu@...dia.com, mperttunen@...dia.com
Subject: Re: [TEGRA194_CPUFREQ Patch 2/3] cpufreq: Add Tegra194 cpufreq driver

On 04-12-19, 16:25, sumitg wrote:
> In T194, CCPLEX doesn't have access to set clocks and the
> 
> clk_{get|set}_rate() functions set clocks by hook to BPMP R5.
> 
> CPU freq can be directly set by CCPLEX using MSR(NVFREQ_REQ_EL1).
> 
> As DVFS run's on BPMP, another MSR (NVFREQ_FEEDBACK_EL1) is
> 
> used to read the counters and calculate "actual" cpu freq at CCPLEX.
> 
> So, "cpuinfo_cur_freq" node gives the actual cpu frequency and not
> 
> given by node "scaling_cur_freq".

Right, but why can't this be hidden in the CPU's clk driver instead,
so cpufreq driver can just do clk_get_rate() and clk_set_rate() ?

> > 
> > - populating cpufreq table, you can probably add OPPs instead using
> >    the same mechanism
> 
> We are reading available frequencies from BPMP to populate
> 
> cpufreq table and not using static opp table.

Right and lot of other platforms read it from firmware (I believe BBMP
is a firmware here), and create OPPs at runtime. Look at this for
example:

drivers/cpufreq/qcom-cpufreq-hw.c

and search for dev_pm_opp_add().

-- 
viresh