Re: [PATCH v2 0/9] Exynos Adaptive Supply Voltage support

From: Sylwester Nawrocki
Date: Mon Aug 19 2019 - 09:40:07 EST

On 8/19/19 13:25, Viresh Kumar wrote:
> On 19-08-19, 13:16, Sylwester Nawrocki wrote:
>> On 8/19/19 11:09, Viresh Kumar wrote:
>>> Will something like this help ?
>>> This never got merged but the idea was AVS only.
>> It's quite interesting work, it seems to be for a more advanced use case
>> where OPP voltage is being adjusted at runtime.
>> We could use it instead of removing an OPP and then adding with updated
>> voltage. On Exynos there is there is just a need to update OPPs once at boot
>> time, so it is more "static". However the requirements could presumably
>> change in future.
> The API is about changing the values after they are parsed once from DT. You can
> change it once or multiple times depending on the use case.
>> If that's your preference I could switch to that notifier approach.
> You shouldn't be required to use the notifier. Just add the OPP table and update
> the values right after that. So no one would be using the values at that time.

OK, now I see dev_pm_opp_adjust_voltage() actually changes OPP's voltage
and the notifier is optional.

> Will this patchset solve the problems for you and make your DT light weight ?

Unfortunately not, the patch set as I see it is another way of updating
an OPP after it was parsed from DT. OPP remove/add could work equally
well in our use case.

The problem is that we have the information on how to translate the
common OPP voltage to a voltage specific to given silicon encoded jointly
in the ASV tables and the CHIPID registers (efuse/OTP memory).
Additionally, algorithm of selecting ASV data (OPP voltage) based on
the "key" data from registers is not generic, it is usually different
per each SoC type.

I tried to identify some patterns in those tables in order to simplify
possible DT binding, but that was not really successful. I ended up just
keeping whole tables.