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SubjectRe: [PATCH] PM / devfreq: Generic cpufreq governor
On 2018-08-01 09:03, Sudeep Holla wrote:
> On 28/07/18 04:56, Saravana Kannan wrote:
>> Many CPU architectures have caches that can scale independent of the
>> CPUs.
>> Frequency scaling of the caches is necessary to make sure the cache is
>> not
>> a performance bottleneck that leads to poor performance and power. The
>> same
>> idea applies for RAM/DDR.
>>
>> To achieve this, this patch adds a generic devfreq governor that can
>> listen
>> to the frequency transitions of each CPU frequency domain and then
>> adjusts
>> the frequency of the cache (or any devfreq device) based on the
>> frequency
>> of the CPUs.
>>
>> To decide the frequency of the device, the governor does one of the
>> following:
>>
>> * Uses a CPU frequency to device frequency mapping table
>> - Either one mapping table used for all CPU freq policies (typically
>> used
>> for system with homogeneous cores/clusters that have the same
>> OPPs.
>> - One mapping table per CPU freq policy (typically used for ASMP
>> systems
>> with heterogeneous CPUs with different OPPs)
>>
>> OR
>>
>> * Scales the device frequency in proportion to the CPU frequency. So,
>> if
>> the CPUs are running at their max frequency, the device runs at its
>> max
>> frequency. If the CPUs are running at their min frequency, the
>> device
>> runs at its min frequency. And interpolated for frequencies in
>> between.
>>
>
> Is this solution for the old generation of SDM ?

This code isn't even specific to Qualcomm chips. Let alone a specific
generation of SDM.

> I have seen newer ones have some kind of firmware interface/hardware to
> deal with CPUFreq. Do you need this solution for them too ?

You are confusing two completely unrelated drivers. This is generic
*devfreq* *governor* code. I'll be renaming the commit text like Rafael
suggested.

Something like: CPU frequency to devfreq mapping governor.

> If yes, why ?

Read the commit text.

> IMO firmware can arbitrate various requests for frequency
> scaling and do the *right thing* for the platform.

Firmware (if any) can arbitrate HW that it controls. DDR and
interconnect is not something a firmware might control (or should
control).

> Having OSPM sending
> separate requests for such bus/interconnect might end up with
> conflicts.
> No ?

If some chips have firmware that takes care of everything, then you
obviously won't be enabling any power management code.

Thanks,
Saravana


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