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Subject: Re: [TEGRA194_CPUFREQ Patch 2/3] cpufreq: Add Tegra194 cpufreq driver
To:     Viresh Kumar <viresh.kumar@linaro.org>
CC:     <rjw@rjwysocki.net>, <catalin.marinas@arm.com>, <will@kernel.org>,
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From:   sumitg <sumitg@nvidia.com>
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Date:   Wed, 4 Dec 2019 16:25:57 +0530
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Hi Viresh,

On 04/12/19 11:10 AM, Viresh Kumar wrote:
> Hi Sumit,
>
> On 03-12-19, 23:02, Sumit Gupta wrote:
>> Add support for CPU frequency scaling on Tegra194. The frequency
>> of each core can be adjusted by writing a clock divisor value to
>> an MSR on the core. The range of valid divisors is queried from
>> the BPMP.
>>
>> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>   drivers/cpufreq/Kconfig.arm        |   6 +
>>   drivers/cpufreq/Makefile           |   1 +
>>   drivers/cpufreq/tegra194-cpufreq.c | 423 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 430 insertions(+)
>>   create mode 100644 drivers/cpufreq/tegra194-cpufreq.c
> Overall these are the things that you are doing here in the driver:
>
> - open coded clk_{get|set}_rate(), why can't you implement a clock
>    driver for the CPU and use the clk framework? You may not need the
>    (hacky) work-queue usage then probably.

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".

>
> - 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.

>
> - And then you can reuse the cpufreq-dt driver for your platform as
>    well, as is the case for few other tegra platforms.
>