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

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Date:   Tue, 20 Aug 2019 08:31:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>, krzk@...nel.org,
        robh+dt@...nel.org, vireshk@...nel.org, devicetree@...r.kernel.org,
        kgene@...nel.org, pankaj.dubey@...sung.com,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, b.zolnierkie@...sung.com
Subject: Re: [PATCH v2 0/9] Exynos Adaptive Supply Voltage support

On 19-08-19, 15:39, Sylwester Nawrocki wrote:
> 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.

Adding OPPs dynamically has limitations, you can't set many values which are
otherwise possible with DT. And removing/adding is not the right thing to do
technically.

> 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.

Sorry but I am unable to understand the difficulty you are facing now. So what I
suggest is something like this.

- Use DT to get a frequency and voltage for each frequency.
- At runtime, based on SoC, registers, efuses, etc, update the voltage of the
  OPPs.
- This algo can be different for each SoC, no one is stopping you from doing
  that.

Am I missing something ?

-- 
viresh