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

From: Sylwester Nawrocki <s.nawrocki@samsung.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
	krzk@kernel.org, robh+dt@kernel.org, vireshk@kernel.org,
	devicetree@vger.kernel.org, kgene@kernel.org,
	pankaj.dubey@samsung.com, linux-samsung-soc@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	b.zolnierkie@samsung.com
Subject: Re: [PATCH v2 0/9] Exynos Adaptive Supply Voltage support
Date: Mon, 19 Aug 2019 15:39:54 +0200	[thread overview]
Message-ID: <b7093aaf-ea56-c390-781f-6f9d0780bd8e@samsung.com> (raw)
In-Reply-To: <20190819112533.bvfyinw7fsebkufr@vireshk-i7>

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 ?
>>>
>>> https://lore.kernel.org/lkml/1442623929-4507-3-git-send-email-sboyd@codeaurora.org/
>>>
>>> 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.

--
Regards, 
Sylwester