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

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Date:   Thu, 25 Jul 2019 07:53:43 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Sylwester Nawrocki <s.nawrocki@...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 24-07-19, 15:10, Marek Szyprowski wrote:
> Hi Viresh,
> 
> On 2019-07-23 04:04, Viresh Kumar wrote:
> > On 18-07-19, 16:30, Sylwester Nawrocki wrote:
> >> This is second iteration of patch series adding ASV (Adaptive Supply
> >> Voltage) support for Exynos SoCs. The first one can be found at:
> >> https://lore.kernel.org/lkml/20190404171735.12815-1-s.nawrocki@samsung.com
> >>
> >> The main changes comparing to the first (RFC) version are:
> >>   - moving ASV data tables from DT to the driver,
> >>   - converting the chipid and the ASV drivers to use regmap,
> >>   - converting the ASV driver to proper platform driver.
> >>
> >> I tried the opp-supported-hw bitmask approach as in the Qualcomm CPUFreq
> >> DT bindings but it resulted in too many OPPs and DT nodes, around 200
> >> per CPU cluster. So the ASV OPP tables are now in the ASV driver, as in
> >> downstream kernels.
> > Hmm. Can you explain why do you have so many OPPs? How many
> > frequencies do you actually support per cluster and what all varies
> > per frequency based on hw ? How many hw version do u have ?
> 
> For big cores there are 20 frequencies (2100MHz .. 200MHz). Each SoC 
> might belong to one of the 3 production 'sets' and each set contains 14 
> so called 'asv groups', which assign the certain voltage values for each 
> of those 20 frequencies (the lower asv group means lower voltage needed 
> for given frequency).

There is another property which might be useful in this case:
"opp-microvolt-<name>" and then you can use API
dev_pm_opp_set_prop_name() to choose which voltage value to apply to
all OPPs.

opp-supported-hw property is more useful for the cases where only a
subset of frequencies will be supported for different versions of the
SoC. And what you need is a different voltage value for all
frequencies based on some h/w version.

-- 
viresh